Errai is a GWT-based framework for building rich web applications using next-generation web technologies. Built on-top of ErraiBus, the framework provides a unified federation and RPC infrastructure with true, uniform, asynchronous messaging across the client and server.
Errai requires a JDK version 6 or higher and depends on Apache Maven to build and run the examples, and for leveraging the quickstart utilities.
Errai is a framework which combines a constellation of web and server-side technologies to assist you in developing large, scaleable rich web applications using a consistent, standardized programming model for client and server development.
Since Errai is an end-to-end framework, in that, parts of the framework run and operate within the client and parts run and operate within the server, there is a set of various technologies upon which Errai relies. This section will detail the basic core technologies which you’ll need to be familiar with.
GWT is a toolkit built around a Java-to-JavaScript compiler. It provides a JRE emulation library, abstraction of browser quirks, a development mode runtime, and tools for native JavaScript integration.
Errai uses GWT to accomplish the translation of concepts such as CDI into the browser, which enables a consistent client and server programming experience.
CDI is a standard part of the Java EE 6.0 stack, and is defined in the JSR-299 specification. CDI is the main programming model explored in this guide. As such, the basic concepts of CDI will be introduced in this guide, so pre-existing knowledge is not strictly necessary.
Errai’s support for CDI is two-fold. For the server-side, Errai has integration with Weld, which is the reference implementation (RI) of the JSR-299 specification. The client-side integration for CDI is provided by the Errai CDI extension. Errai CDI implements a subset of the JSR-299 specification to provide the CDI programming model within client code.
JAX-RS is an API which provides a standardized programming model for specifying web services based around the concept of the Representational State Transfer (REST) architecture. REST has by and far become the preferred way of developing web services, and is used pervasively in modern web applications. Errai provides a set of tools to make working with JAX-RS easier.
The first thing you’ll need to do if you have not already, is install Maven . If you have not already installed Maven, do so now.
Warning: If you use maven2, you will run into this problem: https://community.jboss.org/thread/177645
You have two options to set up an Errai application. You can start by copying an existing example application (i.e. the errai tutorial demo) or by building an app with the Errai Forge Addon:
Simply download and unzip this demo. Check out the README file and continue with running the app in GWT’s development mode and importing the project into Eclipse .
Another way to start a new project with Errai is to use Forge and the Errai Forge Addon. To use this method, follow the instructions here to install the Errai Forge Addon and create a new project.
In the upcomming sections, we will demonstrate how to run your app in GWT Development Mode through the command line and eclipse, so it would be nice to have something to run so that you are able to verify that everything is working. Here is a sample class you can use that displays an alert when the app loads:
// Add the package declaration here
import javax.annotation.PostConstruct;
import org.jboss.errai.ioc.client.api.EntryPoint;
import com.google.gwt.user.client.Window;
@EntryPoint
public class App {
@PostConstruct
public void onLoad() {
Window.alert("Hello World!");
}
}
For this code to run properly, you must use the the Errai Forge Addon Add Errai Features command to install Errai IOC.
Create new subfolder, client/local, under the folder containing your GWT module file. Then create a file, App.java, in this new package and copy the above sample code (making sure to replace the top comment with the package declaration).
Keep an eye out for tips in the proceeding sections on how you can use the Errai Forge plugin to configure other Errai features for your new project.
GWT’s development mode allows for code-refresh development cycles. Simply change a client-side class and refresh the browser to see your changes. You can also debug client and server side code in your IDE of choice.
Change into the newly created project directory and type the following:
mvn clean gwt:run
This will begin the download of all the dependencies required to develop with and run Errai. It may take a few minutes to complete the download.
When it is finished, you should see the GWT Development Mode runtime window appear as shown in Figure 1 running on Windows.
Next, click the Launch Default Browser button. If you have have never used GWT before on your computer, you may get an error when your browser loads as shown in Figure 2 .
Click the blue button that says Download the GWT Developer Plugin to download the plugin. Run the installer to install the plugin for your browser.
If you get a 404 Error for Internet Explorer when clicking the link, you can download the latest plugin for your browser directly from these links:
Once you have configured your browser for development with GWT, and after loading the app with the Launch Default Browser button, you should see the application load.
If you are using errai-tutorial, you should see a page with a complaint form.
If you followed the instructions for using the Errai Forge plugin, there should be a blank page with an alert saying "Hello World!".
That’s it! You’ve got your first Errai Application up and running. In the next section we’ll setup your IDE.
This next section assumes you have followed the instructions in the previous section. As such, we assume you have created an Errai project using the Errai Forge plugin or a copy of the errai-tutorial project, which we’ll be importing into your IDE.
The project that was made in the last section is a Maven project. Thus, we will be relying on Maven to manage our project model throughout this guide. As such, we will want to install Maven tooling in the IDE. If you have not already installed m2e in Eclipse, you will want to do so now.
To install the Maven tooling, use the following steps:
Go to the Eclipse Marketplace under the Help menu in Eclipse.
In the Find dialog enter the phrase Maven and hit enter.
Find the Maven Integration for Eclipse plugin and click the Install button for that entry.
Once you have completed the installation of the prerequisites from the previous section, you will now be able to go ahead and import the Maven project you created in the first section of this guide. We will use the errai-tutorial project as an example.
Follow these steps to get the project setup:
From the File menu, select Import…
You will be presented with the Import dialog box. From here you want to select Maven → Existing Maven Projects
From the Import Maven Projects dialog, you will need to select the directory location of the project you created in the first section of this guide. In the Root Directory field of the dialog, enter the path to the project, or click Browse… to select it from the file chooser dialog.
When the import process has finished, you should see your project imported within the Eclipse Project Explorer . If you are using errai-tutorial, the App
class should be visible within the client
package.
Next you will need to setup a Maven Run Profile for Development Mode. To do so select Run As… > Run Configurations… from the toolbar.
Select Maven Build from the sidebar and create a new launch configuration by pressing the New button in the top left corner.
Give the configuration a name, then click Browse Workspace and select the root directory of your new project.
In the Goals text box, type "clean gwt:run". Click Apply to save the configuration and then Close.
You can add this new configuration under the Run As button in your toolbar by selecting Run As > Organize Favorites, then clicking Add and selecting the run configuration.
At this point, you should try running your new configuration to make sure everything is in working order. To run your app, find the run configuration under the Run As menu in the toolbar.
This will start the GWT Development Mode exactly as running mvn clean gwt:run
from the command line.
To setup a debug run configuration for GWT Development Mode, repeate steps (2) and (3) from the section above, but this time use the Goals "clean gwt:debug".
Next we will need to setup our remote debugger configurations in Eclipse. Because the client and server code run on separate JVMs, we will need to setup two such configurations. To create a debug configuration, select Debug As… > Debug Configurations… from the toolbar.
In the sidebar, select Remote Java Application and click the New button in the top right corner.
This new configuration will be for remote debugging your client-side code, so give it an appropriate name. If the name of your project is not already in the Project field, click Browse and select it. The Host and Port values should be localhost and 8000 respectively, such that your configuration looks like this:
If everything is correct, click Apply.
Create another Remote Java Application run configuration with the steps just described for remote debugging server code. The only differences from the client configuration should be the name and the port, which is 8001. Thus the server remote debug configuration should look like this:
The project you created and setup in the previous two sections (ERRAI:Create your Project and ERRAI:Configuring your project for Eclipse) will be used as the basis for this section. So if you have not read them, do so now.
Use the Errai Forge Addon Add Errai Features command and select Errai CDI to follow along with this section.
Errai CDI as its namesake implies is based on, and is in fact, a partial implementation of the CDI (Contexts and Dependency Injection) specification. Errai CDI covers most of the programming model but omits the CDI SPI, instead replacing it with it a custom set of APIs which are more appropriate for the client programming model of Errai.
These differences aside, using Errai CDI in conjunction with CDI on the server will provide you with a uniform programming model across the client and server code of your application.
This guide does not assume any past experience with CDI. However, you may wish to consider reading the the Weld Documentation in addition to this guide.
A bean in CDI is merely a POJO (Plain Old Java Object), for the most part. In the context of CDI, any plain, default constructable class is a member of the dependent scope . Don’t worry too much about what that means for now. Let’s just go ahead and make one:
public class Foo {
public String getName() {
return "Mr. Foo";
}
}
That was an easy, if uninteresting, exercise. But despite this class' worthy distinction as a dependent-scoped bean, it’s actually quite a useless dependent scope beaned. Well, maybe not so much useless as it is unused.
Well, how would we use this bean? To answer that question we’re going to need to introduce the concept of scopes in more detail.
Scopes, put simply, are the context within which beans live. Some scopes are short-lived and some are long-lived. For instance, there are beans which you may only want to create during a request, and beans which you want to live for as long as the application is running.
It turns out that CDI includes a set of default scopes which represent these very things.
We’ll start by taking a look at the application scope , which is lovingly represented by the annotation @ApplicationScoped
. An application-scoped bean is a bean which will live for the entire duration of the application. In this sense, it is essentially like a singleton. And it’s generally okay to think of it in that way.
So let’s declare an application-scoped bean:
@ApplicationScoped
public class Bar {
public String getName() {
return "Mr. Bar";
}
}
That was almost as easy as making the last bean. The difference between this bean and the last, is Bar
will actually be instantiated by the container automatically, and Foo
will not.
So what can we do with Foo
? Well, let’s go ahead and get familiar with dependency injection, shall we?
@ApplicationScoped
public class Bar {
@Inject Foo foo;
public String getName() {
return "Mr. Bar";
}
}
We have added a field of the type Foo
which we declared earlier, and we have annotated it with javax.inject.Inject
. This tells the container to inject an instance of Foo
into our bean. Since our Foo
bean is of the dependent scope, the bean manager will actually create a new instance of Foo
and pass it in.
This scope of the newly instantiated Foo
is dependent on the scope that it was injected into. In this case, the application scope. On the other hand, if we were to turn around an inject Bar
into Foo
, the behaviour is quite different.
public class Foo {
@Inject Bar bar;
public String getName() {
return "Mr. Foo";
}
}
Here, every time a new instance of Foo
is created, the same instance of Bar
will be injected. That is to say: this pseudo-code assertion is now always true:
assert fooInstance.bar.foo == fooInstance
This identity check will not actually be true at runtime due to the need to proxy the class in this scenario. But it is true, that fooInstance
and fooInstance.bar.foo
both point to the same underlying bean instance.
In the case of an Errai application, there are a bunch of application scoped beans which come built-in for common services like ErraiBus. Thus, in an Errai application which uses the message bus, we can inject a handle to the MessageBus
service into any of our beans. Let’s go ahead and do that in our Bar
class:
@ApplicationScoped
public class Bar {
@Inject Foo foo;
@Inject MessageBus bus;
public String getName() {
return "Mr. Bar";
}
}
If working with dependency injection is new to you, then this is where you’ll start seeing some practical benefit. When you need a common service in your client code, you ask the container for it by injecting it. This frees you from worrying about the proper APIs to use in order to access a service; we need to use the message bus in our Bar
bean, and so we inject it.
Now that we’re getting the gist of how dependency injection works, let’s go back to our sample project.
In the App
class that was created you may have noticed that the bean’s scope is @EntryPoint
.
The @EntryPoint
annotation is an annotation which provides a an analogue to the GWT EntryPoint concept within the context of CDI in Errai. Basically you want to think of @EntryPoint
beans as the Errai CDI-equalivalent of main()
methods. But as of Errai 2.2., that might actually be going a little far. In fact, you might be asking what is the real difference between @ApplicationScoped
and @EntryPoint
in practice. The short answer is: nothing.
When Errai IOC, the technology which powers Errai’s client-side CDI, was first built, it lacked the concept of scopes. To create entry point objects into the application which would automatically run, this annotation was added.
If you’re not convinced, try running this example with the mvn clean gwt:run
command (described above).
Please note, that when launching maven the first time on your machine, it will fetch all dependencies from a central repository. This may take a while, because it includes downloading large binaries like GWT SDK. However, subsequent builds are not required to go through this step and will be much faster.
This section covers the core messaging concepts of the ErraiBus messaging framework.
ErraiBus provides a straight-forward approach to a complex problem space. Providing common APIs across the client and server, developers will have no trouble working with complex messaging scenarios such as building instant messaging clients, stock tickers, to monitoring instruments. There’s no more messing with RPC APIs, or unwieldy AJAX or COMET frameworks. We’ve built it all in to one concise messaging framework. It’s single-paradigm, and it’s fun to work with.
It’s important to understand the concept of how messaging works in ErraiBus. Here are some important facts you’ll need to know:
It can be tempting to think of ErraiBus simply as a client-server communication platform, but there is a plethora of possibilities for using ErraiBus purely within the GWT client context, such as a way to advertise and expose components dynamically, to get around the lack of reflection in GWT.
So keep that in mind when you run up against problems in the client space that could benefit from runtime federation.
Use the Errai Forge Addon Add Errai Features command and select Errai Messaging to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add messaging to your project.
The MessageBuilder is the heart of the messaging API in ErraiBus. It provides a fluent / builder API, that is used for constructing messages. All three major message patterns can be constructed from the MessageBuilder
.
Components that want to receive messages need to implement the MessageCallback
interface.
But before we dive into the details, let’s look at some use cases.
In order to send a message from a client you need to create a Message
and send it through an instance of MessageBus
. In this simple example we send it to the subject HelloWorldService.
public class HelloWorld implements EntryPoint {
// Get an instance of the RequestDispatcher
private RequestDispatcher dispatcher = ErraiBus.getDispatcher();
public void onModuleLoad() {
Button button = new Button("Send message");
button.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
// Send a message to the 'HelloWorldService'.
MessageBuilder.createMessage()
.toSubject("HelloWorldService") // (1)
.signalling() // (2)
.noErrorHandling() // (3)
.sendNowWith(dispatcher); // (4)
});
[...]
}
}
}
In the above example we build and send a message every time the button is clicked. Here’s an explanation of what’s going on as annotated above:
HelloWorldService
".ErrorCallback
to deal with errors for this message.RequestDispatcher
An astute observer will note that access to the RequestDispatcher
differs within client code and server code. Because this client code does not run within a container, access to the RequestDispatcher
and MessageBus
is provided statically using the ErraiBus.get()
and ErraiBus.getDispatcher()
methods. See the section on Errai IOC and Errai CDI for using ErraiBus from a client-side container.
When using Errai IOC or CDI, you can also use the Sender<T> interface to send messages.
Every message has a sender and at least one receiver. A receiver is as it sounds—it receives the message and does something with it. Implementing a receiver (also referred to as a service) is as simple as implementing our standard MessageCallback interface, which is used pervasively across, both client and server code. Let’s begin with server side component that receives messages:
@Service
public class HelloWorldService implements MessageCallback {
public void callback(Message message) {
System.out.println("Hello, World!");
}
}
Here we declare an extremely simple service. The @Service
annotation provides a convenient, meta-data based way of having the bus auto-discover and deploy the service.
In the following example we extend our server side component to reply with a message when the callback method is invoked. It will create a message and address it to the subject ' HelloWorldClient
':
@Service
public class HelloWorldService implements MessageCallback {
private RequestDispatcher dispatcher;
@Inject
public HelloWorldService(RequestDispatcher dispatcher) {
dispatcher = dispatcher;
}
public void callback(CommandMessage message) {
// Send a message to the 'HelloWorldClient'.
MessageBuilder.createMessage()
.toSubject("HelloWorldClient") // (1)
.signalling() // (2)
.with("text", "Hi There") // (3)
.noErrorHandling() // (4)
.sendNowWith(dispatcher); // (5)
});
}
}
The above example shows a service which sends a message in response to receiving a message. Here’s what’s going on:
HelloWorldClient
". We are sending this message to all clients which are listening in on this subject. For information on how to communicate with a single client, see Section 2.6.ErrorCallback
to deal with errors for this message.RequestDispatcher
.Messages can be received asynchronously and arbitriraily by declaring callback services within the client bus. As ErraiBus maintains an open COMET channel at all times, these messages are delivered in real time to the client as they are sent. This provides built-in push messaging for all client services.
public class HelloWorld implements EntryPoint {
private MessageBus bus = ErraiBus.get();
public void onModuleLoad() {
[...]
/*
* Declare a service to receive messages on the subject
* "BroadcastReceiver".
*/
bus.subscribe("BroadcastReceiver", new MessageCallback() {
public void callback(CommandMessage message) {
/*
* When a message arrives, extract the "text" field and
* do something with it
*/
String messageText = message.get(String.class, "text");
}
});
[...]
}
}
In the above example, we declare a new client service called "BroadcastReceiver"
which can now accept both local messages and remote messages from the server bus. The service will be available in the client to receive messages as long the client bus is and the service is not explicitly de-registered.
On the client or the server, you can create a local receiver which only receives messages that originated on the local bus. A local server-side service only receives messages that originate on that server, and a local client-side service only receives messages that originated on that client.
To create a local receiver using the declarative API, use the @Local
annotation in conjunction with @Service
:
@Local
@Service
public class HelloIntrovertService implements MessageCallback {
public void callback(Message message) {
System.out.println("Hello, me!");
}
}
To create a local receiver using through programmatic service registration, use the subscribeLocal()
method in place of subscribe()
:
public void registerLocalService(MessageBus bus) {
bus.subscribeLocal("LocalBroadcastReceiver", new MessageCallback() {
public void callback(Message message) {
String messageText = message.get(String.class, "text");
}
});
}
Both examples above work in client- and server-side code.
It is possible to contruct a message and a default response handler as part of the MessageBuilder
API. It should be noted, that multiple replies will not be possible and will result an exception if attempted. Using this aspect of the API is very useful for doing simple psuedo-synchronous conversive things.
You can do this by specifying a MessageCallback
using the repliesTo()
method in the MessageBuilder
API after specifying the error handling of the message.
MessageBuilder.createMessage()
.toSubject("ConversationalService").signalling()
.with("SomeField", someValue)
.noErrorHandling()
.repliesTo(new MessageCallback() {
public void callback(Message message) {
System.out.println("I received a response");
}
})
See the next section on how to build conversational services that can respond to such messages.
It is possible for the sender to infer, to whatever conversational service it is calling, what subject it would like the reply to go to. This is accomplished by utilizing the standard MessageParts.ReplyTo
message part. Using this methodology for building conversations is generally encouraged.
Consider the following client side code:
MessageBuilder.createMessage()
.toSubject("ObjectService").signalling()
.with(MessageParts.ReplyTo, "ClientEndpoint")
.noErrorHandling().sendNowWith(dispatcher);
And the conversational code on the server (for service ObjectService ):
MessageBuilder.createConversation(message)
.subjectProvided().signalling()
.with("Records", records)
.noErrorHandling().reply();
In the above examples, assuming that the latter example is inside a service called " ObjectService
" and is referencing the incoming message that was sent in the former example, the message created will automatically reference the ReplyTo
subject that was provided by the sender, and send the message back to the subject desired by the client on the client that sent the message.
Broadcasting messages to all clients listening on a specific subject is quite simple and involves nothing more than forgoing use of the reply API. For instance:
MessageBuilder.createMessage().
.toSubject("MessageListener")
.with("Text", "Hello, from your overlords in the cloud")
.noErrorHandling().sendGlobalWith(dispatcher);
If sent from the server, all clients currently connected, who are listening to the subject "MessageListener"
will receive the message. It’s as simple as that.
Communication from one client to another client is not directly possible within the bus federation, by design. This isn’t to say that it’s not possible. But one client cannot see a service within the federation of another client. We institute this limitation as a matter of basic security. But many software engineers will likely find the prospects of such communication appealing, so this section will provide some basic pointers on how to go about accomplishing it.
The essential architectural thing you’ll need to do is create a relay service that runs on the server. Since a service advertised on the server is visible to all clients and all clients are visible to the server, you might already see where we’re going with this.
By creating a service on the server which accepts messages from clients, you can create a simple protocol on-top of the bus to enable quasi peer-to-peer communication. (We say quasi, because it still needs to be routed through the server)
While you can probably imagine simply creating a broadcast-like service which accepts a message from one client and broadcasts it to the rest of the world, it may be less clear how to go about routing from one particular client to another particular client, so we’ll focus on that problem. This is covered in the next chapter.
Every message that is sent between a local and remote (or server and client) buses contain session routing information. This information is used by the bus to determine what outbound queues to use to deliver the message to, so they will reach their intended recipients. It is possible to manually specify this information to indicate to the bus, where you want a specific message to go.
You can obtain the SessionID
directly from a Message
by getting the QueueSession
resource:
QueueSession sess = message.getResource(QueueSession.class, Resources.Session.name());
String sessionId = sess.getSessionId();
You can extract the SessionID
from a message so that you may use it for routing by obtaining the QueueSession
resource from the Message
. For example:
...
public void callback(Message message) {
QueueSession sess = message.getResource(QueueSession.class, Resources.Session.name());
String sessionId = sess.getSessionId();
// Record this sessionId somewhere.
...
}
The SessionID
can then be stored in a medium, say a Map, to cross-reference specific users or whatever identifier you wish to allow one client to obtain a reference to the specific SessionID
of another client. In which case, you can then provide the SessionID
as a MessagePart to indicate to the bus where you want the message to go.
MessageBuilder.createMessage()
.toSubject("ClientMessageListener")
.signalling()
.with(MessageParts.SessionID, sessionId)
.with("Message", "We're relaying a message!")
.noErrorHandling().sendNowWith(dispatcher);
By providing the SessionID
part in the message, the bus will see this and use it for routing the message to the relevant queue.
It may be tempting however, to try and include destination SessionIDs
at the client level, assuming that this will make the infrastructure simpler. But this will not achieve the desired results, as the bus treats SessionIDs
as transient. Meaning, the SessionID
information is not ever transmitted from bus-to-bus, and therefore is only directly relevant to the proximate bus.
Asynchronous messaging necessitates the need for asynchronous error handling. Luckily, support for handling errors is built directly into the MessageBuilder
API, utilizing the ErrorCallback
interface. In the examples shown in previous exceptions, error handing has been glossed over with aubiquitous usage of the noErrorHandling()
method while building messaging. We chose to require the explicit use of such a method to remind developers of the fact that they are responsible for their own error handling, requiring you to explicitly make the decision to forego handling potential errors.
As a general rule, you should always handle your errors . It will lead to faster and quicker identification of problems with your applications if you have error handlers, and generally help you build more robust code.
MessageBuilder.createMessage()
.toSubject("HelloWorldService")
.signalling()
.with("msg", "Hi there!")
.errorsHandledBy(new ErrorCallback() {
public boolean error(Message message, Throwable throwable) {
throwable.printStackTrace();
return true;
}
})
.sendNowWith(dispatcher);
The addition of error handling at first may put off developers as it makes code more verbose and less-readable. This is nothing that some good practice can’t fix. In fact, you may find cases where the same error handler can appropriately be shared between multiple different calls.
ErrorCallback error = new ErrorCallback() {
public boolean error(Message message, Throwable throwable) {
throwable.printStackTrace();
return true;
}
}
MessageBuilder.createMessage()
.toSubject("HelloWorldService")
.signalling()
.with("msg", "Hi there!")
.errorsHandledBy(error)
.sendNowWith(dispatcher);
The error handler is required to return a boolean
value. This is to indicate whether or not Errai should perform the default error handling actions it would normally take during a failure. You will almost always want to return true
here, unless you are trying to explicitly surpress some undesirably activity by Errai, such as automatic subject-termination in conversations. But this is almost never the case.
You may need to detect problems which occur on the bus at runtime. The client bus API provides a facility for doing this in the org.jboss.errai.bus.client.framework.ClientMessageBus
using the addTransportErrorHandler()
method.
A TransportErrorHandler
is an interface which you can use to define error handling behavior in the event of a transport problem.
For example:
messageBus.addTransportErrorHandler(new TransportErrorHandler() {
public void onError(TransportError error) {
// error handling code.
}
});
The TransportError
interface represents the details of an an error from the bus. It contains a set of methods which can be used for determining information on the initial request which triggered the error, if the error occurred over HTTP or WebSockets, status code information, etc. See the JavaDoc for more information.
In some applications, it may be necessary or desirable to delay transmission of, or continually stream data to a remote client or group of clients (or from a client to the server). In cases like this, you can utilize the replyRepeating()
, replyDelayed()
, sendRepeating()
and sendDelayed()
methods in the MessageBuilder
.
Delayed TasksSending a task with a delay is straight forward. Simply utilize the appropriate method (either replyDelayed()
or sendDelayed()
).
MessageBuilder.createConversation(msg)
.toSubject("FunSubject")
.signalling()
.noErrorHandling()
.replyDelayed(TimeUnit.SECONDS, 5); // sends the message after 5 seconds.
or
MessageBuilder.createMessage()
.toSubject("FunSubject")
.signalling()
.noErrorHandling()
.sendDelayed(requestDispatcher, TimeUnit.SECONDS, 5); // sends the message after 5 seconds.
A repeating task is sent using one of the MessageBuilder’s repeatXXX()
methods. The task will repeat indefinitely until cancelled (see next section).
MessageBuilder.createMessage()
.toSubject("FunSubject")
.signalling()
.withProvided("time", new ResourceProvider<String>() {
SimpleDateFormat fmt = new SimpleDateFormat("hh:mm:ss");
public String get() {
return fmt.format(new Date(System.currentTimeMillis());
}
}
.noErrorHandling()
.sendRepeatingWith(requestDispatcher, TimeUnit.SECONDS, 1); //sends a message every 1 second
The above example sends a message very 1 second with a message part called "time"
, containing a formatted time string. Note the use of the withProvided()
method; a provided message part is calculated at the time of transmission as opposed to when the message is constructed.
Cancelling an Asynchronous TaskA delayed or repeating task can be cancelled by calling the cancel()
method of the AsyncTask
instance which is returned when creating a task. Reference to the AsyncTask object can be retained and cancelled by any other thread.
AsyncTask task = MessageBuilder.createConversation(message)
.toSubject("TimeChannel").signalling()
.withProvided(TimeServerParts.TimeString, new ResourceProvider<String>() {
public String get() {
return String.valueOf(System.currentTimeMillis());
}
}).defaultErrorHandling().replyRepeating(TimeUnit.MILLISECONDS, 100);
...
// cancel the task and interrupt it's thread if necessary.
task.cancel(true);
The ErraiBus maintains it’s own seperate session management on-top of the regular HTTP session management. While the queue sessions are tied to, and dependant on HTTP sessions for the most part (meaning they die when HTTP sessions die), they provide extra layers of session tracking to make dealing with complex applications built on Errai easier.
The lifescyle of a session is bound by the underlying HTTP session. It is also bound by activity thresholds. Clients are required to send heartbeat messages every once in a while to maintain their sessions with the server. If a heartbeat message is not received after a certain period of time, the session is terminated and any resources are deallocated.
One of the things Errai offers is the concept of session and local scopes.
A session scope is scoped across all instances of the same session. When a session scope is used, any parameters stored will be accessible and visible by all browser instances and tabs.
The SessionContext helper class is used for accessing the session scope.
public class TestService implements MessageCallback {
public void callback(final Message message) {
// obtain a reference to the session context by referencing the incoming message.
SessionContext injectionContext = SessionContext.get(message);
// set an attribute.
injectionContext.setAttribute("MyAttribute", "Foo");
}
}
A local scope is scoped to a single browser instance. But not to a single session.
In a browser a local scope would be confined to a tab or a window within a browser. You can store parameters inside a local scope just like with a session by using the LocalContext
helper class.
public class TestService implements MessageCallback {
public void callback(final Message message) {
// obtain a reference to the local context by referencing the incoming message.
LocalContext injectionContext = LocalContext.get(message);
// set an attribute.
injectionContext.setAttribute("MyAttribute", "Foo");
}
}
ErraiBus implements a JSON-based wire protocol which is used for the federated communication between different buses. The protocol specification encompasses a standard JSON payload structure, a set of verbs, and an object marshalling protocol. The protocol is named J.REP. Which stands for JSON Rich Event Protocol.
All wire messages sent across are assumed to be JSON arrays at the outermost element, contained in which, there are 0..n messages. An empty array is considered a no-operation, but should be counted as activity against any idle timeout limit between federated buses.
Example 2.1. Example J.REP Payload
[
{"ToSubject" : "SomeEndpoint", "Value" : "SomeValue" },
{"ToSubject" : "SomeOtherEndpoint", "Value" : "SomeOtherValue"}
]
Here we see an example of a J.REP payload containing two messages. One bound for an endpoint named "SomeEndpoint"
and the other bound for the endpoint "SomeOtherEndpoint"
. They both include a payload element "Value"
which contain strings. Let’s take a look at the anatomy of an individual message.
Example 2.2. An J.REP Message
{
"ToSubject" : "TopicSubscriber",
"CommandType" : "Subscribe",
"Value " : "happyTopic",
"ReplyTo" : "MyTopicSubscriberReplyTo"
}
The message shows a very vanilla J.REP message. The keys of the JSON Object represent individual message parts , with the values representing their corresponding values. The standard J.REP protocol encompasses a set of standard message parts and values, which for the purposes of this specification we’ll collectively refer to as the protocol verbs.
The following table describes all of the message parts that a J.REP capable client is expected to understand:
Part | Required | JSON Type | Description |
---|---|---|---|
| Yes | String | Specifies the subject within the bus, and its federation, which the message should be routed to. |
| No | String | Specifies a command verb to be transmitted to the receiving subject. This is an optional part of a message contract, but is required for using management services |
| No | String | Specifies to the receiver what subject it should reply to in response to this message. |
| No | Any | A recommended but not required standard payload part for sending data to services |
| No | Number | A processing order salience attribute. Messages which specify priority processing will be processed first if they are competing for resources with other messages in flight. Note: the current version of ErraiBus only supports two salience levels (0 and >1). Any non-zero salience in ErraiBus will be given the same priority relative to 0 salience messages |
| No | String | An accompanying error message with any serialized exception |
| No | Object | If applicable, an encoded object representing any remote exception that was thrown while dispatching the specified service |
The table contains a list of reserved subject names used for facilitating things like bus management and error handling. A bus should never allow clients to subscribe to these subjects directly.
Subject | Description |
---|---|
| The self-hosted message bus endpoint on the client |
| The self-hosted message bus endpoint on the server |
| The standard error receiving service for clients |
As this table indicates, the bus management protocols in J.REP are accomplished using self-hosted services. See the section on Bus Management and Handshaking Protocols for details.
There is no real distinction in the J.REP protocol between communication with the server, versus communication with the client. In fact, it assumed from an architectural standpoint that there is no real distinction between a client and a server. Each bus participates in a flat-namespaced federation. Therefore, it is possible that a subject may be observed on both the server and the client.
One in-built assumption of a J.REP-compliant bus however, is that messages are routed within the auspices of session isolation. Consider the following diagram:
It is possible for Client A to send messages to the subjects ServiceA and ServiceB . But it is not possible to address messages to ServiceC . Conversely, Client B can address messages to ServiceC and ServiceB , but not ServiceA .
Federation between buses requires management traffic to negotiate connections and manage visibility of services between buses. This is accomplished through services named ClientBus
and ServerBus
which both implement the same protocol contracts which are defined in this section.
Both bus services share the same management protocols, by implementing verbs (or commands) that perform different actions. These are specified in the protocol with the CommandType
message part. The following table describes these commands:
Table 2.1. Message Parts for Bus Commands:
Command / Verb | Message Parts | Description |
---|---|---|
| N/A | The first message sent by a connecting client to begin the handshaking process. |
|
| A message sent by one bus to another to notify it of its capabilities during handshake (for instance long polling or websockets) |
| N/A | A message sent from one bus to another to indicate that it has now provided all necessary information to the counter-party bus to establish the federation. When both buses have sent this message to each other, the federation is considered active. |
|
| A message sent to the remote bus to notify it of a service or set of services which it is capable of routing to. |
|
| A message sent to the remote bus to notify it that a service is no longer available. |
|
| A message sent to a server bus from a client bus to indicate that it wishes to disconnect and defederate. Or, when sent from the client to server, indicates that the session has been terminated. |
| N/A | A message sent to a client bus to indicate that its messages are no longer being routed because it no longer has an active session |
| N/A | A message sent from one bus to another periodically to indicate it is still active. |
Part | Required | JSON Type | Description |
---|---|---|---|
| Yes | String | A comma delimited string of capabilities the bus is capable of us |
| Yes | String | The subject to subscribe or unsubscribe from |
| Yes | Array | An array of strings representing a list of subjects to subscribe to |
Conversations are message exchanges which are between a single client and a service. They are a fundmentally important concept in ErraiBus, since by default, a message will be broadcast to all client services listening on a particular channel.
When you create a reply with an incoming message, you ensure that the message you are sending back is received by the same client which sent the incoming message. A simple example:
@Service
public class HelloWorldService implements MessageCallback {
public void callback(CommandMessage message) {
// Send a message to the 'HelloWorldClient' on the client that sent us the
// the message.
MessageBuilder.createConversation(message)
.toSubject("HelloWorldClient")
.signalling()
.with("text", "Hi There! We're having a reply!")
.noErrorHandling().reply();
});
}
}
Note that the only difference between the example in the previous section and this is the use of the createConversation()
method with MessageBuilder
.
ErraiBus has support for WebSocket-based communication. When WebSockets are enabled, capable web browsers will attempt to upgrade their COMET-based communication with the server-side bus to use a WebSocket channel.
There are two different ways the bus can enable WebSockets. The first uses a sideband server, which is a small, lightweight server which runs on a different port from the application server. The second is native JBoss AS 7-based integration.
Activating the sideband server is as simple as adding the following to the ErraiService.properties
file:
errai.bus.enable_web_socket_server=true
The default port for the sideband server is 8085
. You can change this by specifying a port with the errai.bus.web_socket_port
property in the ErraiService.properties
file.
Make sure to deploy the required Netty dependencies to your server. If you started with one of our demos or our tutorial project it should be enough to NOT set netty-codec-http
to provided. All required transitive dependencies should then be part of your war file (WEB-INF/lib).
This is an alternative approach to the sideband server described in the previous chapter. Make sure to NOT configure both! It is currently necessary to use the native connector in JBoss AS for WebSockets to work. So the first step is to configure your JBoss AS instance(s) to use the native connector by changing the domain/configuration/standalone.xml
or domain/configuration/domain.xml
file as follows:
<subsystem xmlns="urn:jboss:domain:web:1.1" default-virtual-server="default-host" native="false">
to:
<subsystem xmlns="urn:jboss:domain:web:1.1" default-virtual-server="default-host" native="true">
To verify that the native connectors are being used check your console for the following log message:
INFO [org.apache.coyote.http11.Http11AprProtocol] (MSC service thread 1-6) Starting Coyote HTTP/1.1 on http-/127.0.0.1:8080
The important part is org.apache.coyote.http11.Http11AprProtocol
. You should NOT be seeing org.apache.coyote.http11.Http11Protocol
. You might have to install the Tomcat native library if not already available on your system.
You will then need to configure the servlet in your application’s web.xml
which will provide WebSocket upgrade support within AS7.
Add the following to the web.xml
:
<context-param>
<param-name>websockets-enabled</param-name>
<param-value>true</param-value>
</context-param>
<context-param>
<param-name>websocket-path-element</param-name>
<param-value>in.erraiBusWS</param-value>
</context-param>
This will tell the bus to enable web sockets support. The websocket-path-element
specified the path element within a URL which the client bus should request in order to negotiate a websocket connection. For instance, specifying in.erraiBusWS
as we have in the snippit above, will result in attempted negotiation at http://<your_server>:<your_port>/<context_path>/in.erraiBusWS
. For this to have any meaningful result, we must add a servlet mapping that will match this pattern:
<servlet>
<servlet-name>ErraiWSServlet</servlet-name>
<servlet-class>org.jboss.errai.bus.server.servlet.JBossAS7WebSocketServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>ErraiWSServlet</servlet-name>
<url-pattern>*.erraiBusWS</url-pattern>
</servlet-mapping>
When configuring ErraiBus to use WebSockets on JBoss AS, you do not remove the existing servlet mappings for the bus. The WebSocket servlet is in addition to your current bus servlet. This is because ErraiBus always negotiates WebSocket sessions over the COMET channel.
Also make sure to deploy the required errai-bus-jboss7-websocket.jar to your server. If you’re using Maven simply add the following dependency to your pom.xml file:
<dependency>
<groupId>org.jboss.errai</groupId>
<artifactId>errai-bus-jboss7-websocket</artifactId>
<version>${errai.version}</version>
</dependency>
By default, Errai’s client-side message bus attempts to connect to the server as soon as the ErraiBus module has been loaded. The bus will stay connected until a lengthy (about 45 seconds) communication failure occurs, or the web page is unloaded.
The application can affect bus communication through two mechanisms:
erraiBusRemoteCommunicationEnabled = false
before the GWT scripts load, bus communication with the server is permanently disabled((ClientMessageBus) ErraiBus.get()).stop()
, the bus disconnects from the serverTo resume server communication after a call to ClientMessageBus.stop()
or after communication with the server has exceeded the bus' retry timeout, call ((ClientMessageBus) ErraiBus.get()).init()
. You can use a BusLifecycleListener
to monitor the success or failure of this attempt. See the next section for details.
In a perfect world, the client message bus would always be able to communicate with the server message bus. But in the real world, there’s a whole array of reasons why the communication link between the server and the client might be interrupted.
On its own, the client message bus will attempt to reconnect with the server whenever communication has been disrupted. Errai applications can monitor the status of the bus' communication link (whether it is disconnected, attempting to connect, or fully connected) through the BusLifecycleListener
interface:
class BusStatusLogger implements BusLifecycleListener {
@Override
public void busAssociating(BusLifecycleEvent e) {
GWT.log("Errai Bus trying to connect...");
}
@Override
public void busOnline(BusLifecycleEvent e) {
GWT.log("Errai Bus connected!");
}
@Override
public void busOffline(BusLifecycleEvent e) {
GWT.log("Errai Bus trying to connect...");
}
@Override
public void busDisassociating(BusLifecycleEvent e) {
GWT.log("Errai Bus going into local-only mode.");
}
}
To attach such a listener to the bus, make the following call in client-side code:
ClientMessageBus bus = (ClientMessageBus) ErraiBus.get();
bus.addLifecycleListener(new BusStatusLogger());
Shadow Services is a Service that will get invoked when there is no longer a connection with the server. This is particular helpful when developing an application for mobile. To create a Shadow Service for a specific Services all you have to do is annotate a new client side implementation with the @ShadowService:
@ShadowService
public class SignupShadowService implements MessageCallback {
@Override
public void callback(Message message) {
}
}
Also when you have a RPC based Service you can just add @ShadowService on a client side implementation to configure it to be the service to get called when there is no network:
@ShadowService
public class SignupServiceShadow implements SignupService {
@Override
public User register(User newUserObject, String password) throws RegistrationException {
}
}
In this shadow service we can create logic that will deal with the temporary connection loss. For instance you could save the data that needs to get send to the server with JPA on the client and then when the bus get online again sent the data to the server.
Errai includes a bus monitoring application, which allows you to monitor all of the message exchange activity on the bus in order to help track down any potential problems It allows you to inspect individual messages to examine their state and structure.
To utilize the bus monitor, you’ll need to include the _errai-tools _ package as part of your application’s dependencies. When you run your application in development mode, you will simply need to add the following JVM options to your run configuration in order to launch the monitor: -Derrai.tools.bus_monitor_attach=true
The monitor provides you a real-time perspective on what’s going on inside the bus. The left side of the main screen lists the services that are currently available, and the right side is the service-explorer, which will show details about the service.
To see what’s going on with a specific service, simply double-click on the service or highlight the service, then click "Monitor Service…". This will bring up the service activity monitor.
The service activity monitor will display a list of all the messages that were transmitted on the bus since the monitor became active. You do not need to actually have each specific monitor window open in order to actively monitor the bus activity. All activity on the bus is recorded.
The monitor allows you select individual messages, an view their individual parts. Clicking on a message part will bring up the object inspector, which will allow you to explore the state of any objects contained within the message, not unlike the object inspectors provided by debuggers in your favorite IDE. This can be a powerful tool for looking under the covers of your application.
Use the Errai Forge Addon Add Errai Features command and select Errai IOC to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai IOC to your project.
The core Errai IOC module implements the JSR-330 Dependency Injection specification for in-client component wiring.
Dependency injection (DI) allows for cleaner and more modular code, by permitting the implementation of decoupled and type-safe components. By using DI, components do not need to be aware of the implementation of provided services. Instead, they merely declare a contract with the container, which in turn provides instances of the services that component depends on.
Errai only scans the contents of classpath locations (JARs and directories) that have a file called
ErraiApp.properties at their root. If dependency injection is not working for you, double-check that you have an ErraiApp.properties
in every JAR and directory that contains classes Errai should know about.
A simple example:
public class MyLittleClass {
private final TimeService timeService;
@Inject
public MyLittleClass(TimeService timeService) {
this.timeService = timeService;
}
public void printTime() {
System.out.println(this.timeService.getTime());
}
}
In this example, we create a simple class which declares a dependency using @Inject
for the interface TimeService
. In this particular case, we use constructor injection to establish the contract between the container and the component. We can similarly use field injection to the same effect:
public class MyLittleClass {
@Inject
private TimeService timeService;
public void printTime() {
System.out.println(this.timeService.getTime());
}
}
In order to inject TimeService
, you must annotate it with @ApplicationScoped
or the Errai DI container will not acknowledge the type as a bean.
@ApplicationScoped
public class TimeService {
}
Although field injection results in less code, a major disadvantage is that you cannot create immutable classes using the pattern, since the container must first call the default, no-argument constructor, and then iterate through its injection tasks, which leaves the potential albeit remote that the object could be left in an partially or improperly initialized state. The advantage of constructor injection is that fields can be immutable (final), and invariance rules applied at construction time, leading to earlier failures, and the guarantee of consistent state.
In contrast to Gin , the Errai IOC container does not provide a programmatic way of creating and configuring injectors. Instead, container-level binding rules are defined by implementing a Provider
, which is scanned for and auto-discovered by the container.
A Provider
is essentially a factory which produces type instances within in the container, and defers instantiation responsibility for the provided type to the provider implementation. Top-level providers use the standard javax.inject.Provider<T>
interface.
Types made available as top-level providers will be available for injection in any managed component within the container.
Out of the box, Errai IOC implements these default top-level providers, all defined in the org.jboss.errai.ioc.client.api.builtin
package:
CallerProvider :
Makes RPC Caller<T>
objects available for injection.DisposerProvider :
Makes Errai IoC Disposer<T>
objects available for injection.InitBallotProvider :
Makes instances of InitBallot
available for injection.IOCBeanManagerProvider :
Makes Errai’s client-side bean manager, ClientBeanManager
, available for injection.MessageBusProvider :
Makes Errai’s client-side MessageBus
singleton available for injection.RequestDispatcherProvider :
Makes an instance of the RequestDispatcher
available for injection.RootPanelProvider :
Makes GWT’s RootPanel
singleton injectable.SenderProvider :
Makes MessageBus Sender<T>
objects available for injection.Implementing a Provider
is relatively straight-forward. Consider the following two classes:
TimeService.java
public interface TimeService {
public String getTime();
}
TimeServiceProvider.java
@IOCProvider
@Singleton
public class TimeServiceProvider implements Provider<TimeService> {
@Override
public TimeService get() {
return new TimeService() {
public String getTime() {
return "It's midnight somewhere!";
}
};
}
}
If you are familiar with Guice, this is semantically identical to configuring an injector like so:
Guice.createInjector(new AbstractModule() {
public void configure() {
bind(TimeService.class).toProvider(TimeServiceProvider.class);
}
}).getInstance(MyApp.class);
As shown in the above example code, the annotation @IOCProvider
is used to denote top-level providers.
The classpath will be searched for all annotated providers at compile time.
Top-level providers are regular beans, so they can inject dependencies particularly from other top-level providers as necessary.
By default, Errai uses Google Guice to wire server-side components. When deploying services on the server-side, it is currently possible to obtain references to the MessageBus
, RequestDispatcher
, the ErraiServiceConfigurator
, and ErraiService
by declaring them as injection dependencies in Service classes, extension components, and session providers.
Alternatively, supports CDI based wiring of server-side components. See the chapter on Errai CDI for more information.
Out of the box, the IOC container supports three bean scopes, @Dependent
, @Singleton
and @EntryPoint
. The singleton and entry-point scopes are roughly the same semantics.
In Errai IOC, all client types are valid bean types if they are default constructable or can have construction dependencies satisfied. These unqualified beans belong to the dependent pseudo-scope. See: Dependent Psuedo-Scope from CDI Documentation
Additionally, beans may be qualified as @ApplicationScoped
, @Singleton
or @EntryPoint
. Although @ApplicationScoped
and @Singleton
are supported for completeness and conformance, within the client they effectively result in behavior that is identical.
Example 3.1. Example dependent scoped bean
public void MyDependentScopedBean {
private final Date createdDate;
public MyDependentScopedBean {
createdDate = new Date();
}
}
Example 3.2. Example ApplicationScoped bean
@ApplicationScoped
public void MyClientBean {
@Inject MyDependentScopedBean bean;
// ... //
}
As is mentioned in the bean manager documentation , only beans that are explicitly scoped will be made available to the bean manager for lookup. So while it is not necessary for regular injection, you must annotate your dependent scoped beans with @Dependent
if you wish to dynamically lookup these beans at runtime.
As Errai IOC provides a container-based approach to client development, support for Errai services are exposed to the container so they may be injected and used throughout your application where appropriate. This section covers those services.
The org.jboss.errai.bus.server.annotations.Service
annotation is used for binding service endpoints to the bus. Within the Errai IOC container you can annotate services and have them published to the bus on the client (or on the server) in a very straight-forward manner:
Example 3.3. A simple message receiving service
@Service
public class MyService implements MessageCallback {
public void callback(Message message) {
// ... //
}
}
As with server-side use of the annotation, if a service name is not explicitly specified, the underlying class name or field name being annotated will be used as the service name.
The org.jboss.errai.bus.server.api.Local
annotation is used in conjunction with the @Service
annotation to advertise a service only for visibility on the local bus and thus, cannot receive messages across the wire for the service.
Example 3.4. A local only service
@Service @Local
public class MyLocalService implements MessageCallback {
public void callback(Message message) {
// ... //
}
}
Services which are registered with ErraiBus via the bean manager through use of the @Service
annotation, have de-registration hooks tied implicitly to the destruction of the bean. Thus, destruction of the bean implies that these associated services are to be dereferenced.
The IOC container, by default, provides a set of default injectable bean types. They range from basic services, to injectable proxies for RPC. This section covers the facilities available out-of-the-box.
The type org.jboss.errai.bus.client.framework.MessageBus
is globally injectable into any bean. Injecting this type will provide the instance of the active message bus running in the client.
The type org.jboss.errai.bus.client.framework.RequestDispatcher
is globally injectable into any bean. Injecting this type will provide a RequestDispatcher
instance capable of delivering any messages provided to it, to the the MessageBus
.
The type org.jboss.errai.common.client.api.Caller<?>
is a globally injectable RPC proxy. RPC proxies may be provided by various components. For example, JAX-RS or Errai RPC. The proxy itself is agnostic to the underlying RPC mechanism and is qualified by it’s type parameterization.
For example:
Example 3.7. An example Caller<?> proxy
public void MyClientBean {
@Inject
private Caller<MyRpcInterface> rpcCaller;
// ... ///
@EventHandler("button")
public void onButtonClick(ClickHandler handler) {
rpcCaller.call(new RemoteCallback<Void>() {
public void callback(Void void) {
// put code here that should execute after RPC response arrives
}
).callSomeMethod();
}
}
The above code shows the injection of a proxy for the RPC remote interface, MyRpcInterface
. For more information on defining RPC proxies see Remote Procedure Calls (RPC).
The org.jboss.errai.ioc.support.bus.client.Sender<?>
interface is the lower-level counterpart to the Caller<?>
interface described above. You can inject a Sender
to send low-level ErraiBus messages directly to subscribers on any subject.
For example:
@Inject
@ToSubject("ListCapitializationService")
Sender<List<String>> listSender;
// ... ///
@EventHandler("button")
public void onButtonClick(ClickHandler handler) {
List<String> myListOfStrings = getSelectedCitiesFromForm();
listSender.send(myListOfStrings, new MessageCallback() {
public void callback(Message reply) {
// do stuff with reply
}
);
}
The Sender.send()
method is overloaded. The variant demonstrated above takes a value and a MessageCallback to reply receive a reply (assuming the subscriber sends a conversational reply). The following variants are available:
send(T)
send(T, ErrorCallback)
send(T, MessageCallback)
send(T, MessageCallback, ErrorCallback)
The reply-to service can also be specified declaratively using the @ReplyTo
annotation. This allows the app to receive conversational replies even when using the send()
variants that do not take a MessageCallback
:
@Inject
@ToSubject("ListCapitializationService")
@ReplyTo("ClientListService")
Sender<List<String>> listSender;
// ... ///
@EventHandler("button")
public void onButtonClick(ClickHandler handler) {
List<String> myListOfStrings = getSelectedCitiesFromForm();
listSender.send(myListOfStrings);
}
@Singleton
@Service
public static class ClientListService implements MessageCallback {
@Override
public void callback(Message message) {
// do stuff with message
}
}
These Sender<?>
features are just convenient wrappers around the full-featured programmatic ErraiBus API. See Messaging API Basics and Conversations for full information about low-level ErraiBus communication.
A problem commonly associated with building large applications in the browser is ensuring that things happen in the proper order when code starts executing. Errai IOC provides you tools which permit you to ensure things happen before initialization, and forcing things to happen after initialization of all of the Errai services.
In order to prevent initialization of the the bus and it’s services so that you can do necessary configuration, especially if you are writing extensions to the Errai framework itself, you can create an implicit startup dependency on your bean by injecting an org.jboss.errai.ioc.client.api.InitBallot<?>
.
Example 3.8. Using an InitBallot to Control Startup
@Singleton
public class MyClientBean {
@Inject InitBallot<MyClientBean> ballot;
@PostConstruct
public void doStuff() {
// ... do some work ...
ballot.voteForInit();
}
}
Sending RPC calls to the server from inside constructors and @PostConstruct
methods in Errai is not always reliable due to the fact that the bus and RPC proxies initialize asynchronously with the rest of the application. Therefore it is often desirable to have such things happen in a post-initialization task, which is exposed in the ClientMessageBus
API. However, it is much cleaner to use the @AfterInitialization
annotation on one of your bean methods.
Example 3.9. Using @AfterInitialization to do something after startup
@Singleton
public class MyClientBean {
@AfterInitialization
public void doStuffAfterInit() {
// ... do some work ...
}
}
The @Timed
annotation allows scheduling method executions on managed client-side beans. Timers are automatically scoped to the scope of the corresponding managed bean and participate in the same lifecycle (see Bean Lifecycle for details).
In the following example the updateTime
method is invoked repeatedly every second.
@Timed(type = TimerType.REPEATING, interval = 1, timeUnit = TimeUnit.SECONDS)
private void updateTime() {
timeWidget.setTime(System.currentTimeMillis);
}
For delayed one-time execution of methods type = TimerType.DELAYED
can be used instead.
It may be necessary at times to manually obtain instances of beans managed by Errai IOC from outside the container managed scope or creating a hard dependency from your bean. Errai IOC provides a simple client-side bean manager for handling these scenarios: org.jboss.errai.ioc.client.container.ClientBeanManager
.
As you might expect, you can inject a bean manager instance into any of your managed beans. If you use Errai IOC in its default mode you will need to inject the synchronous bean manager ( org.jboss.errai.ioc.client.container.SyncBeanManager
).
If you have asynchronous IOC mode enabled simply inject the asynchronous bean manager ( org.jboss.errai.ioc.client.container.async.AsyncBeanManager
) instead. Asynchronous IOC brings support for code splitting . That means that any bean annotated with @LoadAsync
can be compiled into a separate JavaScript file that’s downloaded when the bean is first needed on the client. @LoadAsync
also allows to specify a fragment name using a class literal. Using GWT 2.6.0 or higher, all types with the same fragment name will be part of the same JavaScript file.
Example 3.10. Injecting the client-side bean manager
public MyManagedBean {
@Inject SyncBeanManager manager;
// class body
}
If you need to access the bean manager outside a managed bean, such as in a unit test, you can access it by calling org.jboss.errai.ioc.client.container.IOC.getBeanManager()
Looking up beans can be done through the use of the lookupBeans()
method. Here’s a basic example:
Example 3.11. Example lookup of a bean
public MyManagedBean {
@Inject SyncBeanManager manager;
public void lookupBean() {
IOCBeanDef<SimpleBean> bean = manager.lookupBean(SimpleBean.class);
if (bean != null) {
// get the instance of the bean
SimpleBean inst = bean.getInstance();
}
}
}
In this example we lookup a bean class named SimpleBean
. This example will succeed assuming that SimpleBean
is unambiguous. If the bean is ambiguous and requires qualification, you can do a qualified lookup like so:
Example 3.12. Looking up beans with qualifiers
MyQualifier qual = new MyQualifier() {
public annotationType() {
return MyQualifier.class;
}
}
MyOtherQualifier qual2 = new MyOtherQualifier() {
public annotationType() {
return MyOtherQualifier.class;
}
}
// pass qualifiers to ClientBeanManager.lookupBeans
IOCBeanDef<SimpleBean> bean = beanManager.lookupBean(SimpleBean.class, qual, qual2);
In this example we manually construct instances of qualifier annotations in order to pass it to the bean manager for lookup. This is a necessary step since there’s currently no support for annotation literals in Errai client code.
It may be desirable to have multiple matching dependencies for a given injection point with the ability to specify which implementation to use at runtime. For instance, you may have different versions of your application which target different browsers or capabilities of the browser. Using alternatives allows you to share common interfaces among your beans, while still using dependency injection, by exporting consideration of what implementation to use to the container’s configuration.
Consider the following example:
@Singleton @Alternative
public class MobileView implements View {
// ... //
}
and
@Singleton @Alternative
public class DesktopView implements View {
// ... //
In our controller logic we in turn inject the View
interface:
@EntryPoint
public class MyApp {
@Inject
View view;
// ... //
}
This code is unaware of the implementation of View
, which maintains good separation of concerns. However, this of course creates an ambiguous dependency on the View
interface as it has two matching subtypes in this case. Thus, we must configure the container to specify which alternative to use. Also note, that the beans in both cases have been annotated with javax.enterprise.inject.Alternative
.
In your ErraiApp.properties
for the module, you can simply specify which active alternative should be used:
errai.ioc.enabled.alternatives=org.foo.MobileView
You can specify multiple alternative classes by white space separating them:
errai.ioc.enabled.alternatives=org.foo.MobileView \ org.foo.HTML5Orientation \ org.foo.MobileStorage
You can only have one enabled alternative for a matching set of alternatives, otherwise you will get ambiguous resolution errors from the container.
Similar to alternatives, but specifically designed for testing scenarios, you can replace beans with mocks at runtime for the purposes of running unit tests. This is accomplished simply by annotating a bean with the org.jboss.errai.ioc.client.api.TestMock
annotation. Doing so will prioritize consideration of the bean over any other matching beans while running unit tests.
Consider the following:
@ApplicationScoped
public class UserManagementImpl implements UserManagement {
public List<User> listUsers() {
// do user listy things!
}
}
You can specify a mock implementation of this class by implementing its common parent type ( UserManagement
) and annotating that class with the @TestMock
annotation inside your test package like so:
@TestMock @ApplicationScoped
public class MockUserManagementImpl implements UserManagement {
public List<User> listUsers() {
// return only a test user.
return Collections.singletonList(TestUser.INSTANCE);
}
}
In this case, the container will replace the UserManagementImpl
with the MockUserManagementImpl
automatically when running the unit tests.
The @TestMock
annotation can also be used to specify alternative providers during test execution. For example, it can be used to mock a Caller<T>
. Callers
are used to invoke RPC or JAX-RS endpoints. During tests you might want to replace theses callers with mock implementations. For details on providers see Container Wiring .
@TestMock @IOCProvider
public class MockedHappyServiceCallerProvider implements ContextualTypeProvider<Caller<HappyService>> {
@Override
public Caller<HappyService> provide(Class<?>[] typeargs, Annotation[] qualifiers) {
return new Caller<HappyService>() {
...
}
}
All beans managed by the Errai IOC container support the @PostConstruct
and @PreDestroy
annotations.
Beans which have methods annotated with @PostConstruct
are guaranteed to have those methods called before the bean is put into service, and only after all dependencies within its graph has been satisfied.
Beans are also guaranteed to have their @PreDestroy
annotated methods called before they are destroyed by the bean manager.
This cannot be guaranteed when the browser DOM is destroyed prematurely due to: closing the browser window; closing a tab; refreshing the page, etc.
Beans under management of Errai IOC, of any scope, can be explicitly destroyed through the client bean manager. Destruction of a managed bean is accomplished by passing a reference to the destroyBean()
method of the bean manager.
Example 3.13. Destruction of bean
public MyManagedBean {
@Inject SyncBeanManager manager;
public void createABeanThenDestroyIt() {
// get a new bean.
SimpleBean bean = manager.lookupBean(SimpleBean.class).getInstance();
bean.sendMessage("Sorry, I need to dispose of you now");
// destroy the bean!
manager.destroyBean(bean);
}
}
When the bean manager "destroys" the bean, any pre-destroy methods the bean declares are called, it is taken out of service and no longer tracked by the bean manager. If there are references on the bean by other objects, the bean will continue to be accessible to those objects.
Container managed resources that are dependent on the bean such as bus service endpoints or CDI event observers will also be automatically destroyed when the bean is destroyed.
Another important consideration is the rule, "all beans created together are destroyed together." Consider the following example:
Example 3.14. SimpleBean.class
@Dependent
public class SimpleBean {
@Inject @New AnotherBean anotherBean;
public AnotherBean getAnotherBean() {
return anotherBean;
}
@PreDestroy
private void cleanUp() {
// do some cleanup tasks
}
}
Example 3.15. Destroying bean from subgraph
public MyManagedBean {
@Inject SyncBeanManager manager;
public void createABeanThenDestroyIt() {
// get a new bean.
SimpleBean bean = manager.lookupBean(SimpleBean.class).getInstance();
// destroy the AnotherBean reference from inside the bean
manager.destroyBean(bean.getAnotherBean());
}
}
In this example we pass the instance of AnotherBean,
created as a dependency of SimpleBean,
to the bean manager for destruction. Because this bean was created at the same time as its parent, its destruction will also result in the destruction of SimpleBean
; thus, this action will result in the @PreDestroy
[code]cleanUp()
method of SimpleBean
being invoked.
Another way which beans can be destroyed is through the use of the injectable org.jboss.errai.ioc.client.api.Disposer<T>
class. The class provides a straight forward way of disposing of bean type.
For instance:
Example 3.16. Destroying bean with disposer
public MyManagedBean {
@Inject @New SimpleBean myNewSimpleBean;
@Inject Disposer<SimpleBean> simpleBeanDisposer;
public void destroyMyBean() {
simpleBeanDisposer.dispose(myNewSimpleBean);
}
}
Use the Errai Forge Addon Add Errai Features command and select Errai CDI to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai CDI to your project.
CDI (Contexts and Dependency Injection) is the Jave EE standard (JSR-299) for handling dependency injection. In addition to dependency injection, the standard encompasses component lifecycle, application configuration, call-interception and a decoupled, type-safe eventing specification.
The Errai CDI extension implements a subset of the specification for use inside of client-side applications within Errai, as well as additional capabilities such as distributed eventing.
Errai CDI does not currently implement all life cycles specified in JSR-299 or interceptors. These deficiencies may be addressed in future versions.
Errai CDI is implemented as an extension on top of the Errai IOC Framework (see Dependency Injection), which itself implements JSR-330. Inclusion of the CDI module your GWT project will result in the extensions automatically being loaded and made available to your application.
Errai CDI only scans the contents of classpath locations (JARs and directories) that have a file called
ErraiApp.properties at their root. If CDI features such as dependency injection, event observation, and @PostConstruct
are not working for your classes, double-check that you have an ErraiApp.properties
at the root of every JAR and directory tree that contains classes Errai should know about.
Beans that are deployed to a CDI container will automatically be registered with Errai and exposed to your GWT client application. So, you can use Errai to communicate between your GWT client components and your CDI backend beans.
Errai CDI based applications use the same annotation-driven programming model as server-side CDI components, with some notable limitations. Many of these limitations will be addressed in future releases.
@Typed
annotation is unsupported.@Interceptor
annotation is unsupported.@Decorator
annotation is unsupported.The CDI container in Errai is built around the Errai IOC module , and thus is a superset of the existing functionality in Errai IOC. Thus, all features and APIs documented in Errai IOC are accessible and usable with this Errai CDI programming model.
Any CDI managed component may produce and consume events . This allows beans to interact in a completely decoupled fashion. Beans consume events by registering for a particular event type and optional qualifiers. The Errai CDI extension simply extends this concept into the client tier. A GWT client application can simply register an Observer
for a particular event type and thus receive events that are produced on the server-side. Likewise and using the same API, GWT clients can produce events that are consumed by a server-side observer.
Let’s take a look at an example.
Example 4.1. FraudClient.java
public class FraudClient extends LayoutPanel {
@Inject
private Event<AccountActivity> event; (1)
private HTML responsePanel;
public FraudClient() {
super(new BoxLayout(BoxLayout.Orientation.VERTICAL));
}
@PostConstruct
public void buildUI() {
Button button = new Button("Create activity", new ClickHandler() {
public void onClick(ClickEvent clickEvent) {
event.fire(new AccountActivity());
}
});
responsePanel = new HTML();
add(button);
add(responsePanel);
}
public void processFraud(@Observes @Detected Fraud fraudEvent) { (2)
responsePanel.setText("Fraud detected: " + fraudEvent.getTimestamp());
}
}
Two things are noteworthy in this example:
Event
dispatcher proxyObserver
method for a particular event typeThe event dispatcher is responsible for sending events created on the client-side to the server-side event subsystem (CDI container). This means any event that is fired through a dispatcher will eventually be consumed by a CDI managed bean, if there is an corresponding Observer
registered for it on the server side.
In order to consume events that are created on the server-side you need to declare an client-side observer method for a particular event type. In case an event is fired on the server this method will be invoked with an event instance of type you declared.
To complete the example, let’s look at the corresponding server-side CDI bean:
Example 4.2. AccountService.java
@ApplicationScoped
public class AccountService {
@Inject @Detected
private Event<Fraud> event;
public void watchActivity(@Observes AccountActivity activity) {
Fraud fraud = new Fraud(System.currentTimeMillis());
event.fire(fraud);
}
}
A server can address a single client in response to an event annotating event types as @Conversational
. Consider a service that responds to a subscription event.
Example 4.3. SubscriptionService.java
@ApplicationScoped
public class SubscriptionService {
@Inject
private Event<Documents> welcomeEvent;
public void onSubscription(@Observes Subscription subscription) {
Document docs = createWelcomePackage(subscription);
welcomeEvent.fire(docs);
}
}
And the Document
class would be annotated like so:
As such, when Document
events are fired, they will be limited in scope to the initiating conversational contents which are implicitly inferred by the caller. So only the client which fired the Subscription
event will receive the fired Document
event.
A key feature of the Errai CDI framework is the ability to federate the CDI eventing bus between the client and the server. This permits the observation of server produced events on the client, and vice-versa.
Example server code:
Example 4.5. MyServerBean.java
@ApplicationScoped
public class MyServerBean {
@Inject
Event<MyResponseEvent> myResponseEvent;
public void myClientObserver(@Observes MyRequestEvent event) {
MyResponseEvent response;
if (event.isThankYou()) {
// aww, that's nice!
response = new MyResponseEvent("Well, you're welcome!");
}
else {
// how rude!
response = new MyResponseEvent("What? Nobody says 'thank you' anymore?");
}
myResponseEvent.fire(response);
}
}
Domain-model:
Example 4.6. MyRequestEvent.java
@Portable
public class MyRequestEvent {
private boolean thankYou;
public MyRequestEvent(boolean thankYou) {
setThankYou(thankYou);
}
public void setThankYou(boolean thankYou) {
this.thankYou = thankYou;
}
public boolean isThankYou() {
return thankYou;
}
}
Example 4.7. MyResponseEvent.java
@Portable
public class MyResponseEvent {
private String message;
public MyRequestEvent(String message) {
setMessage(message);
}
public void setMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
Client application logic:
Example 4.8. MyClientBean.java
@EntryPoint
public class MyClientBean {
@Inject
Event<MyRequestEvent> requestEvent;
public void myResponseObserver(@Observes MyResponseEvent event) {
Window.alert("Server replied: " + event.getMessage());
}
@PostConstruct
public void init() {
Button thankYou = new Button("Say Thank You!");
thankYou.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
requestEvent.fire(new MyRequestEvent(true));
}
}
Button nothing = new Button("Say nothing!");
nothing.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
requestEvent.fire(new MyRequestEvent(false));
}
}
VerticalPanel vPanel = new VerticalPanel();
vPanel.add(thankYou);
vPanel.add(nothing);
RootPanel.get().add(vPanel);
}
}
Producer methods and fields act as sources of objects to be injected. They are useful when additional control over object creation is needed before injections can take place e.g. when you need to make a decision at runtime before an object can be created and injected.
Example 4.9. App.java
@EntryPoint
public class App {
...
@Produces @Supported
private MyBaseWidget createWidget() {
return (Canvas.isSupported()) ? new MyHtml5Widget() : new MyDefaultWidget();
}
}
Example 4.10. MyComposite.java
@ApplicationScoped
public class MyComposite extends Composite {
@Inject @Supported
private MyBaseWidget widget;
...
}
Producers can also be scoped themselves. By default, producer methods are dependent-scoped, meaning they get called every time an injection for their provided type is requested. If a producer method is scoped @Singleton
for instance, the method will only be called once, and the bean manager will inject the instance from the first invokation of the producer into every matching injection point.
Example 4.11. Singleton producer
public class App {
...
@Produces @Singleton
private MyBean produceMyBean() {
return new MyBean();
}
}
For more information on CDI producers, see the CDI specification and the WELD reference documentation .
As an alternative to using the bean manager to dynamically create beans, this can be accomplished in a type-safe way by injecting a javax.enterprise.inject.Instance<T>
.
For instance, assume you have a dependent-scoped bean Bar
and consider the following:
public class Foo {
@Inject Instance<Bar> barInstance;
public void pingNewBar() {
Bar bar = barInstance.get();
bar.ping();
}
}
In this example, calling barInstance.get()
returns a new instance of the dependent-scoped bean Bar
.
The CDI integration is a plugin to the Errai core framework and represents a CDI portable extension. Which means it is discovered automatically by both Errai and the CDI container. In order to use it, you first need to understand the different runtime models involved when working GWT, Errai, and CDI.
Typically a GWT application lifecycle begins in Development Mode and finally a web application containing the GWT client code will be deployed to a target container (Servlet Engine, Application Server). This is no way different when working with CDI components to back your application.
What’s different however is availability of the CDI container across the different runtimes. In GWT development mode and in a pure servlet environment you need to provide and bootstrap the CDI environment on your own. While any Java EE 6 Application Server already provides a preconfigured CDI container. To accomodate these differences, we need to do a little trickery when executing the GWT Development Mode and packaging our application for deployment.
Use the Errai Forge Addon Add Errai in Project command to setup development mode, usable for any Errai application, including one with Errai CDI.
Checkout the Manual Setup Section for instructions on how to manually setup Errai CDI in Development Mode.
Errai includes a comprehensive marshalling framework which permits the serialization of domain objects between the browser and the server. From the perspective of GWT, this is a complete replacement for the provided GWT serialization facilities and offers a great deal more flexibility. You are be able to map both application-specific domain model, as well as preexisting model, including model from third-party libraries using the custom definitions API.
If you used the Errai Forge Addon Add Errai Features command to add Errai Messaging or Errai CDI then Marshalling is already available to you.
All classes that you intend to be marshalled between the client and the server must be exposed to the marshalling framework. There are several ways you can do it and this section will take you through the different approaches you can take to fit your needs.
To make a Java class eligible for serialization with Errai Marshalling, mark it with the org.jboss.errai.common.client.api.annotations.Portable
annotation. This tells the marshalling system to generate marshalling and demarshalling code for the annotated class and all of its nested classes.
The mapping strategy that will be used depends on how much information you provide about your model up-front. If you simply annotate a domain type with @Portable
and do nothing else, the marshalling system will use and exhaustive strategy to determine how to construct and deconstruct instances of that type and its nested types.
The Errai marshalling system works by enumerating all of the Portable types it can find (by any of the three methods discussed in this section of the reference guide), eliminating all the non-portable types it can find (via @NonPortable
annotations and entries in ErraiApp.properties
), then enumerating the marshallable properties that make up each remaining portable entity type. The rules that Errai uses for enumerating the properties of a portable entity type are as follows:
foo
, then that entity has a property called foo
unless the field is marked static
or transient
.Note that the existence of methods called getFoo()
, setFoo()
, or both, does not mean that the entity has a property called foo
. Errai Marshalling always works from fields when discovering properties.
When reading a field foo
, Errai Marshalling will call the method getFoo()
in preference to direct field access if the getFoo()
method exists.
Similarly, when writing a field foo
, Errai Marshalling will call the method setFoo()
in preference to direct field access if the setFoo()
method exists.
The above rules are sufficient for marshalling an existing entity to a JSON representation, but for de-marshalling, Errai must also know how to obtain an instance of a type. The rules that Errai uses for deciding how to create an instance of a @Portable
type are as follows:
@MapsTo
, and those parameters cover all properties of the entity type, then Errai uses this constructor to create the object, passing in all of the property values.@MapsTo
, and those parameters cover all properties of the entity type, then Errai uses this method to create the object. Note that when using this mechanism you are free to create and return a subtype of the marshalled type, or resolve one from a cache.Now let’s take a look at some common examples of how this works.
@Portable
public class Person {
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
This is a pretty vanilla domain object. Note the default, public, no-argument constructor. In this case, it will be necessary to have one explicitly declared. But notice we have no setters. In this case, the marshaler will rely on private field access to write the values on each side of the marshalling transaction. For simple domain objects, this is both nice and convenient. But you may want to make the class immutable and have a constructor enforce invariance. See the next section for that.
Immutability is almost always a good practice, and the marshalling system provides you a straight forward way to tell it how to marshal and de-marshal objects which enforce an immutable contract. Let’s modify our example from the previous section.
@Portable
public class Person {
private final String name;
private final int age;
public Person(@MapsTo("name") String name, @MapsTo("age") int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
Here we have set both of the class fields final. By doing so, we had to remove our default constructor. But that’s okay, because we have annotated the remaining constructor’s parameters using the org.jboss.errai.marshalling.client.api.annotations.MapsTo
annotation.
By doing this, we have told the marshaling system, for instance, that the first parameter of the constructor maps to the property name
. Which in this case, defaults to the name of the corresponding field. This may not always be the case as will be explored in the section on custom definitions. But for now that’s a safe assumption.
Another good practice is to use a factory pattern to enforce invariance. Once again, let’s modify our example.
@Portable
public class Person {
private final String name;
private final int age;
private Person(String name, int age) {
this.name = name;
this.age = age;
}
public static Person createPerson(@MapsTo("name") String name, @MapsTo("age") int age) {
return new Person(name, age);
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
Here we have made our only declared constructor private, and created a static factory method. Notice that we’ve simply used the same @MapsTo
annotation in the same way we did on the constructor from our previous example. The marshaller will see this method and know that it should use it to construct the object.
For types with a large number of optional attributes, a builder is often the best approach.
@Portable
public class Person {
private final String name;
private final int age;
private Person(@MapsTo("name") String name, @MapsTo("age") int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@NonPortable
public static class Builder {
private String name;
private int age;
public Builder name(String name) {
this.name = name;
return this;
}
public Builder age(int age) {
this.age = age;
return this;
}
public Person build() {
return new Person(name, age);
}
}
}
In this example, we have a nested Builder
class that implements the Builder Pattern and calls the private Person
constructor. Hand-written code will always use the builder to create Person
instances, but the @MapsTo
annotations on the private Person
constructor tell Errai Marshalling to bypass the builder and construct instances of Person directly.
One final note: as a nested type of Person
(which is marked @Portable
), the builder itself would normally be portable. However, we do not intend to move instances of Person.Builder
across the network, so we mark Person.Builder
as @NonPortable
.
Some classes may be out of your control, making it impossible to annotate them for auto-discovery by the marshalling framework. For cases such as this, there are two approaches which can be undertaken to include these classes in your application.
The first approach is the easiest, but is contingent on whether or not the class is directly exposed to the GWT compiler. That means, the classes must be part of a GWT module and within the GWT client packages. See the GWT documentation on Client-Side Code for information on this.
If you have client-exposed classes that cannot be annotated with the @Portable
annotation, you may manually map these classes so that the marshaller framework will comprehend and produce marshallers for them and their nested types.
To do this, specify them in ErraiApp.properties , using the errai.marshalling.serializableTypes
attribute with a whitespace separated list of classes to make portable.
Example 5.1. Example ErraiApp.properties defining portable classes.
errai.marshalling.serializableTypes=org.foo.client.UserEntity \ org.foo.client.GroupEntity \ org.abcinc.model.client.Profile
If any of the serializable types have nested classes that you wish to make non-portable, you can specify them like this:
Example 5.2. Example ErraiApp.properties defining nonportable classes.
errai.marshalling.nonserializableTypes=org.foo.client.UserEntity$Builder \ org.foo.client.GroupEntity$Builder
The marshalling framework supports and promotes the concept of marshalling by interface contract, where possible. For instance, the framework ships with a marshaller which can marshall data to and from the java.util.List
interface. Instead of having custom marshallers for classes such as ArrayList
and LinkedList
, by default, these implementations are merely aliased to the java.util.List
marshaller.
There are two distinct ways to go about doing this. The most straightforward is to specify which marshaller to alias when declaring your class is @Portable
.
package org.foo.client;
@Portable(aliasOf = java.util.List.class)
public MyListImpl extends ArrayList {
// .. //
}
In the case of this example, the marshaller will not attempt to comprehend your class. Instead, it will merely rely on the java.util.List
marshaller to dematerialize and serialize instances of this type onto the wire.
If for some reason it is not feasible to annotate the class, directly, you may specify the mapping in the ErraiApp.properties file using the errai.marshalling.mappingAliases
attribute.
errai.marshalling.mappingAliases=org.foo.client.MyListImpl->java.util.List \ org.foo.client.MyMapImpl->java.util.Map
The list of classes is whitespace-separated so that it may be split across lines.
The example above shows the equivalent mapping for the MyListImpl
class from the previous example, as well as a mapping of a class to the java.util.Map
marshaller.
The syntax of the mapping is as follows: <class_to_map>
→[code]<contract_to_map_to>
.
When you alias a class to another marshalling contract, extended fields of the aliased class will not be available upon deserialization. For this you must provide custom marshallers for those classes.
Although the default marshalling strategies in Errai Marshalling will suit the vast majority of use cases, there may be situations where it is necessary to manually map your classes into the marshalling framework to teach it how to construct and deconstruct your objects.
This is accomplished by specifying MappingDefinition
classes which inform the framework exactly how to read and write state in the process of constructing and deconstructing objects.
All manual mappings should extend the org.jboss.errai.marshalling.rebind.api.model.MappingDefinition
class. This is base metadata class which contains data on exactly how the marshaller can deconstruct and construct objects.
Consider the following class:
public class MySuperCustomEntity {
private final String mySuperName;
private String mySuperNickname;
public MySuperCustomEntity(String mySuperName) {
this.mySuperName = mySuperName;;
}
public String getMySuperName() {
return this.mySuperName;
}
public void setMySuperNickname(String mySuperNickname) {
this.mySuperNickname = mySuperNickname;
}
public String getMySuperNickname() {
return this.mySuperNickname;
}
}
Let us construct this object like so:
MySuperCustomEntity entity = new MySuperCustomEntity("Coolio");
entity.setSuperNickname("coo");
It is clear that we may rely on this object’s two getter methods to extract the totality of its state. But due to the fact that the mySuperName
field is final, the only way to properly construct this object is to call its only public constructor and pass in the desired value of mySuperName
.
Let us consider how we could go about telling the marshalling framework to pull this off:
@CustomMapping
public MySuperCustomEntityMapping extends MappingDefinition {
public MySuperCustomEntityMapping() {
super(MySuperCustomEntity.class); // (1)
SimpleConstructorMapping cnsMapping = new SimpleConstructorMapping();
cnsMapping.mapParmToIndex("mySuperName", 0, String.class); // (2)
setInstantiationMapping(cnsMapping);
addMemberMapping(new WriteMapping("mySuperNickname", String.class, "setMySuperNickname")); // (3)
addMemberMapping(new ReadMapping("mySuperName", String.class, "getMySuperName")); // (4)
addMemberMapping(new ReadMapping("mySuperNickname", String.class, "getMySuperNickname")); // (5)
}
}
And that’s it. This describes to the marshalling framework how it should go about constructing and deconstructing MySuperCustomEntity
.
Paying attention to our annotating comments, let’s describe what we’ve done here.
MappingDefinition
passing our reference to the class we are mapping.SimpleConstructorMapping
class, we have indicated that a custom constructor will be needed to instantiate this class. We have called the mapParmToIndex
method with three parameters. The first, "mySupername"
describes the class field that we are targeting. The second parameter, the integer 0
indicates the parameter index of the constructor arguments that we’ll be providing the value for the aforementioned field in this case the first and only, and the final parameter String.class
tells the marshalling framework which marshalling contract to use in order to de-marshall the value.WriteMapping
class, we have indicated to the marshaller framework how to write the "mySuperNickname"
field, using the String.class
marshaller, and using the setter method setMySuperNickname
.ReadMapping
class, we have indicated to the marshaller framework how to read the "mySuperName"
field, using the String.class
marshaller, and using the getter method getMySuperName
.ReadMapping
class, we have indicated to the marshaller framework how to read the "mySuperNickname"
field, using the String.class
marshaller, and using the getter method getMySuperNickname
.There is another approach to extending the marshalling functionality that doesn’t involve mapping rules, and that is to implement your own Marshaller
class. This gives you complete control over the parsing and emission of the JSON structure.
The implementation of marshallers is made relatively straight forward by the fact that both the server and the client share the same JSON parsing API.
Consider the included java.util.Date
marshaller that comes built-in to the marshalling framework:
Example 5.3. DataMarshaller.java from the built-in marshallers
@ClientMarshaller(Date.class)
@ServerMarshaller(Date.class)
public class DateMarshaller extends AbstractNullableMarshaller<Date> {
@Override
public Date[] getEmptyArray() {
return new Date[0];
}
@Override
public Date doNotNullDemarshall(final EJValue o, final MarshallingSession ctx) {
if (o.isObject() != null) {
EJValue qualifiedValue = o.isObject().get(SerializationParts.QUALIFIED_VALUE);
if (!qualifiedValue.isNull() && qualifiedValue.isString() != null) {
return new Date(Long.parseLong(qualifiedValue.isString().stringValue()));
}
EJValue numericValue = o.isObject().get(SerializationParts.NUMERIC_VALUE);
if (!numericValue.isNull() && numericValue.isNumber() != null) {
return new Date(new Double(numericValue.isNumber().doubleValue()).longValue());
}
if (!numericValue.isNull() && numericValue.isString() != null) {
return new Date(Long.parseLong(numericValue.isString().stringValue()));
}
}
return null;
}
@Override
public String doNotNullMarshall(final Date o, final MarshallingSession ctx) {
return "{\"" + SerializationParts.ENCODED_TYPE + "\":\"" + Date.class.getName() + "\"," +
"\"" + SerializationParts.OBJECT_ID + "\":\"" + o.hashCode() + "\"," +
"\"" + SerializationParts.QUALIFIED_VALUE + "\":\"" + o.getTime() + "\"}";
}
}
The class is annotated with both @ClientMarshaller
and @ServerMarshaller
indicating that this class should be used for both marshalling on the client and on the server.
The doNotNullDemarshall()
method is responsible for converting the given JSON object (which has already been parsed and verified non-null) into a Java object.
The doNotNullMarshall()
method does roughly the inverse: it converts the given Java object into a String (which must be parseable as a JSON object) for transmission on the wire.
ErraiBus supports a high-level RPC layer to make typical client-server RPC communication easy on top of the bus. While it is possible to use ErraiBus without ever using this API, you may find it to be a more useful and concise approach for exposing services to the clients.
Please note that this API has changed since version 1.0. RPC services provide a way of creating type-safe mechanisms to make client-to-server calls. Currently, this mechanism only support client-to-server calls, and not vice-versa.
Using the Errai Forge Addon Add Errai Features command, Errai RPC can be used if Errai Messaging or Errai CDI have been installed.
Checkout the Manual Setup Section for instructions on how to manually add Errai Messaging or Errai CDI to a project.
Creating a service is straight forward. It requires the definition of a remote interface, and a service class which implements it. See the following:
@Remote
public interface MyRemoteService {
public boolean isEveryoneHappy();
}
The @Remote
annotation tells Errai that we’d like to use this interface as a remote interface. The remote interface must be part of of the GWT client code. It cannot be part of the server-side code, since the interface will need to be referenced from both the client and server side code. That said, the implementation of a service is relatively simple to the point:
@Service
public class MyRemoteServiceImpl implements MyRemoteService {
public boolean isEveryoneHappy() {
// blatently lie and say everyone's happy.
return true;
}
}
That’s all there is to it. You use the same @Service
annotation as described in Section 2.4. The presence of the remote interface tips Errai off as to what you want to do with the class.
Beginning with Errai 2.0.CR1, the default for automatic service discovery has changed in favour of CDI based applications, meaning RPC service discovery must be explicitly turned on in case Errai CDI is not used (the weld-integration.jar
is not on the classpath). This can be done using an init-param in the servlet config of your web.xml:
<servlet>
<servlet-name>ErraiServlet</servlet-name>
<servlet-class>org.jboss.errai.bus.server.servlet.DefaultBlockingServlet</servlet-class>
<init-param>
<param-name>auto-discover-services</param-name>
<param-value>true</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
Calling a remote service involves use of the MessageBuilder
API. Since all messages are asynchronous, the actual code for calling the remote service involves the use of a callback, which we use to receive the response from the remote method. Let’s see how it works:
MessageBuilder.createCall(new RemoteCallback<Boolean>() {
public void callback(Boolean isHappy) {
if (isHappy) Window.alert("Everyone is happy!");
}
}, MyRemoteService.class).isEveryoneHappy();
In the above example, we declare a remote callback that receives a Boolean, to correspond to the return value of the method on the server. We also reference the remote interface we are calling, and directly call the method. However, don’t be tempted to write code like this :
boolean bool = MessageBuilder.createCall(..., MyRemoteService.class).isEveryoneHappy();
The above code will never return a valid result. In fact, it will always return null, false, or 0 depending on the type. This is due to the fact that the method is dispatched asynchronously, as in, it does not wait for a server response before returning control. The reason we chose to do this, as opposed to emulate the native GWT-approach, which requires the implementation of remote and async interfaces, was purely a function of a tradeoff for simplicity.
An alternative to using the MessageBuilder
API is to have a proxy of the service injected.
@Inject
private Caller<MyRemoteService> remoteService;
For calling the remote service, the callback objects need to be provided to the call
method before the corresponding interface method is invoked.
remoteService.call(callback).isEveryoneHappy();
The Errai IOC GWT module needs to be inherited to make use of caller injection. To do this, the following line needs to be added to the application’s \*.gwt.xml
file. It is important that this line comes after
the Errai Bus module:
<inherits name="org.jboss.errai.ioc.Container"/>
Handling remote exceptions can be done by providing an ErrorCallback
on the client:
MessageBuilder.createCall(
new RemoteCallback<Boolean>() {
public void callback(Boolean isHappy) {
if (isHappy) Window.alert("Everyone is happy!");
}
},
new ErrorCallback() {
public boolean error(Message message, Throwable caught) {
try {
throw caught;
}
catch (NobodyIsHappyException e) {
Window.alert("OK, that's sad!");
}
catch (Throwable t) {
GWT.log("An unexpected error has occurred", t);
}
return false;
}
},
MyRemoteService.class).isEveryoneHappy();
As remote exceptions need to be serialized to be sent to the client, the @Portable
annotation needs to be present on the corresponding exception class (see Marshalling>). Further the exception class needs to be part of the client-side code. For more details on ErrorCallbacks
see <<sid-5931306, Handling Errors .
In a scenario where many different remote calls potentially throw the same exception types (e.g. exceptions related to authentication or authorization) it can be easier to register a global exception handler instead of providing error callbacks at each RPC invocation. This global exception handler is called in case an exception occurs in the process of a remote call that has no error callback associated with it. So, it will handle an otherwise uncaught exception.
@UncaughtException
private void onUncaughtException(Throwable caught) {
try {
throw caught;
}
catch (UserNotLoggedInException e) {
// navigate to login dialog
}
catch (Throwable t) {
GWT.log("An unexpected error has occurred", t);
}
}
Client-side remote call interceptors provide the ability to manipulate or bypass the remote call before it’s being sent. This is useful for implementing crosscutting concerns like caching, for example when the remote call should be avoided if the data is already cached locally.
To have a remote call intercepted, either an interface method or the remote interface type has to be annotated with @InterceptedCall
. If the type is annotated, all interface methods will be intercepted.
@Remote
public interface CustomerService {
@InterceptedCall(MyCacheInterceptor.class)
public Customer retrieveCustomerById(long id);
}
Note that an ordered list of interceptors can be used for specifying an interceptor chain e.g.
@InterceptedCall({MyCacheInterceptor.class, MySecurityInterceptor.class})
public Customer retrieveCustomerById(long id);
Implementing an interceptor is easy:
public class MyCacheInterceptor implements RpcInterceptor {
@Override
public void aroundInvoke(final RemoteCallContext context) {
// e.g check if the result is cached and carry out the actual call only in case it's not.
context.proceed() // executes the next interceptor in the chain or the actual remote call.
// context.setResult() // sets the result directly without carrying out the remote call.
}
}
The RemoteCallContext
passed to the aroundInvoke
method provides access to the intercepted method’s name and read/write access to the parameter values provided at the call site.
Calling proceed
executes the next interceptor in the chain or the actual remote call if all interceptors have already been executed. If access to the result of the (asynchronous) remote call is needed in the interceptor, one of the overloaded versions of proceed
accepting a RemoteCallback
has to be used instead.
The result of the remote call can be manipulated by calling RemoteCallContext.setResult()
.
Not calling proceed
in the interceptor bypasses the actual remote call, passing RestCallContext.getResult()
to the RemoteCallBack
provided at the call site.
If you cannot (or do not wish to) annotate the remote interface you may instead define remote call interceptors by annotating the interceptor class itself with @InterceptsRemoteCall
. This annotation requires the developer to specify the remote interface that should be intercepted. The interceptor will then be applied to all methods in that interface. If the interface method is annotated with InterceptedCall
, that annotation will win out.
@InterceptsRemoteCall({ MyRemoteInterface.class, MyOtherRemoteInterface.class })
public class CustomRpcInterceptor implements RpcInterceptor {
@Override
public void aroundInvoke(final RemoteCallContext context) {
// interceptor logic goes here
}
}
This approach sacrifices granularity (you cannot intercept individual methods on the remote interface). However, it does allow method interception without modification to the remote interface (which is particularly useful when the developer is not in control of the remote interface).
It is worth noting that interceptors may be defined as managed beans using the @Dependent
, @Singleton
, or @ApplicationScoped
annotations. If the Errai application is using IOC (i.e. imports the IOC Errai module) and the interceptor is annotated as a managed bean, then the IOC container will be used to get/create the interceptor instance. This allows developers to @Inject
dependencies into interceptors. If IOC is not being used, or else the interceptor is not properly annotated, then the interceptor class will simply be instantiated via new.
Before invoking an endpoint method Errai sets up an RpcContext
that provides access to message resources that are otherwise not visible to RPC endpoints.
@Service
public class MyRemoteServiceImpl implements MyRemoteService {
public boolean isEveryoneHappy() {
HttpSession session = RpcContext.getHttpSession();
ServletRequest request = RpcContext.getServletRequest();
...
return true;
}
}
Some use cases require multiple interactions with the server to complete. Errai’s RPC mechanism allows for batched invocations of remote methods that will be executed using a single server round-trip. This is useful for reducing the number of simultaneous HTTP connections and at the same time allows for reusing and combining fine-grained remote services.
Injecting a BatchCaller instead of a Caller<T> is all it takes to make use of batched remote procedure calls.
@EntryPoint
public class MyBean {
@Inject
private BatchCaller batchCaller;
private void someMethod() {
// ...
batchCaller.call(remoteCallback1, RemoteService1.class).method1();
batchCaller.call(remoteCallback2, RemoteService2.class).method2();
// Invokes the accumulated remote requests using a single server round-trip.
batchCaller.sendBatch();
}
}
The remote methods will get executed only after sendBatch()
was called. The method sendBatch
accepts an additional RemoteCallback
instance as a parameter which will we invoked when all remote calls have completed in success. Consequently, an ErrorCallback
can also be provided which will get executed for all remote calls that have completed in failure.
If computing the result of an RPC call takes a significant amount of time (i.e. because a third party service needs to be contacted or a long running query needs to be executed) it might be preferable to release the request-processing thread so it can perform other work and provide the result in a different execution context farther in the future. So, the RPC endpoint method can return immediately and the thread handling the incoming request doesn’t need to stay active until the result is available. Computing and setting the result can be done in a different thread (i.e. from a smaller thread pool provided by a library).
Errai provides a special return type CallableFuture
to indicate to the RPC system that the result of the remote method call will be provided asynchronously (after the remote method call has returned).
Here’s an example returning a result of type String:
@Remote
public interface LongRunningService {
public CallableFuture<String> someLongRunningTask();
}
@Service
public class LongRunningServiceImpl implements LongRunningService {
@Override
public CallableFuture<String> someLongRunningTask() {
final CallableFuture<String> future = CallableFutureFactory.get().createFuture(String.class);
final ExecutorService executorService = Executors.newSingleThreadExecutor();
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
future.setValue("result");
}
catch (Throwable t) {
t.printStackTrace();
}
}
});
executorService.shutdown();
return future;
}
}
Note that the client-side code does not change when using this feature and will work exactly as described in Section 6.2, “Making calls” i.e.:
MessageBuilder.createCall(new RemoteCallback<String>() {
@Override
public void callback(String response) {
assertEquals("foobar", response);
finishTest();
}
}, LongRunningService.class).someLongRunningTask();
JAX-RS (Java API for RESTful Web Services) is a Java EE standard (JSR-311) for implementing REST-based Web services in Java. Errai JAX-RS brings this standard to the browser and simplifies the integration of REST-based services in GWT client applications. Errai can generate proxies based on JAX-RS interfaces which will handle all the underlying communication and serialization logic. All that’s left to do is to invoke a Java method.
Errai’s JAX-RS support consists of the following:
@Inject
instances of {{Caller<T>} (the same API used in Errai RPC)}Use the Errai Forge Addon Add Errai Features command and select Errai JAXRS to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add JAX-RS to your project. You can also go to the Errai tutorial project or the demo collection for an example of JAX-RS.
Errai’s JAX-RS support consists mostly of features that make the client side easier and more reliable to maintain. You will need to use an existing third-party JAX-RS implementation on the server side. All Java EE 6 application servers include such a module out-of-the-box. If you are developing an application that you intend to deploy on a plain servlet container, you will have to choose a JAX-RS implementation (for example, RestEasy) and configure it properly in your web.xml.
Alternatively, you could keep your REST resource layer in a completely separate web application hosted on the same server (perhaps build an Errai JAX-RS client against an existing REST service you developed previously). In this case, you could factor out the shared JAX-RS interface into a shared library, leaving the implementation in the non-Errai application.
Finally, you can take advantage of the cross-origin resource sharing (CoRS) feature in modern browsers and use Errai JAX-RS to send requests to a third-party server. The third-party server would have to be configured to allow cross-domain requests. In this case, you would write a JAX-RS-Annotated interface describing the remote REST resources, but you would not create an implementation of that interface.
Errai JAX-RS works by leveraging standard Java interfaces that bear JAX-RS annotations. You will also want these interfaces visible to server-side code so that your JAX-RS resource classes can implement them (and inherit the annotations). This keeps the whole setup typesafe, and reduces duplication to the bare minimum. The natural solution, then is to put the JAX-RS interfaces under the client.shared package within your GWT module:
project
src/main/java
com.mycompany.myapp
com.mycompany.myapp.client.local
com.mycompany.myapp.client.shared
com.mycompany.myapp.server
The contents of the server-side files would be as follows:
Example 7.1. CustomerService.java
@Path("customers")
public interface CustomerService {
@GET
@Produces("application/json")
public List<Customer> listAllCustomers();
@POST
@Consumes("application/json")
@Produces("text/plain")
public long createCustomer(Customer customer);
}
The above interface is visible both to server-side code and to client-side code. It is used by client-side code to describe the available operations, their parameter types, and their return types. If you use your IDE’s refactoring tools to modify this interface, both the server-side and client-side code will be updated automatically.
Example 7.2. CustomerServiceImpl.java
public class CustomerServiceImpl implements CustomerService {
@Override
public List<Customer> listAllCustomers() {
// Use a database API to look up all customers in back-end data store
// Return the resulting list
}
@Override
public long createCustomer(Customer customer) {
// Store new Customer instance in back-end data store
}
}
The above class implements the shared interface. Since it performs database and/or filesystem operations to manipulate the persistent data store, it is not GWT translatable, and it’s therefore kept in a package that is not part of the GWT module.
Note that all JAX-RS annotations ( @Path
, @GET
, @Consumes
, and so on) can be inherited from the interface. You do not need to repeat these annotations in your resource implementation classes.
This section assumes you have already set up the CustomerService JAX-RS endpoint as described in the previous section.
To create a request on the client, all that needs to be done is to invoke RestClient.create()
, thereby providing the JAX-RS interface, a response callback and to invoke the corresponding interface method:
Example 7.3. App.java
...
Button create = new Button("Create", new ClickHandler() {
public void onClick(ClickEvent clickEvent) {
Customer customer = new Customer(firstName, lastName, postalCode);
RestClient.create(CustomerService.class, callback).createCustomer(customer);
}
});
...
For details on the callback mechanism see Handling Responses .
Injectable proxies can be used as an alternative to calling RestClient.create()
.
@Inject
private Caller<CustomerService> customerService;
To create a request, the callback objects need to be provided to the call
method before the corresponding interface method is invoked.
customerService.call(callback).listAllCustomers();
To use caller injection, your application needs to inherit the Errai IOC GWT module. To do this, just add this line to your application’s \*.gwt.xml
file and make sure it comes after
the Errai JAX-RS module (see Getting Started ):
<inherits name="org.jboss.errai.ioc.Container"/>
The JAX-RS interfaces need to be visible to the GWT compiler and must therefore reside within the client packages (e.g. client.shared).
An instance of Errai’s RemoteCallback<T>
has to be passed to the RestClient.create()
call, which will provide access to the JAX-RS resource method’s result. T
is the return type of the JAX-RS resource method. In the example below it’s just a Long
representing a customer ID, but it can be any serializable type (see Marshalling).
RemoteCallback<Long> callback = new RemoteCallback<Long>() {
public void callback(Long id) {
Window.alert("Customer created with ID: " + id);
}
};
A special case of this RemoteCallback
is the ResponseCallback
which can be used as an alternative. It provides access to the Response
object representing the underlying HTTP response. This is useful when more details of the HTTP response are needed, such as headers and the status code. The ResponseCallback
can also be used for JAX-RS interface methods that return a javax.ws.rs.core.Response
type. In this case, the MarshallingWrapper
class can be used to manually demarshall the response body to an entity of the desired type.
ResponseCallback callback = new ResponseCallback() {
public void callback(Response response) {
Window.alert("HTTP status code: " + response.getStatusCode());
Window.alert("HTTP response body: " + response.getText());
}
};
For handling errors, Errai’s error callback mechanism can be reused and an instance of ErrorCallback
can optionally be passed to the RestClient.create()
call. In case of an HTTP error, the ResponseException
provides access to the Response
object. All other Throwables
indicate a communication problem.
ErrorCallback errorCallback = new RestErrorCallback() {
public boolean error(Request request, Throwable throwable) {
try {
throw throwable;
}
catch (ResponseException e) {
Response response = e.getResponse();
// process unexpected response
response.getStatusCode();
}
catch (Throwable t) {
// process unexpected error (e.g. a network problem)
}
return false;
}
};
To provide more customized error handling, Errai also defines client side exception handling via the ClientExceptionMapper
interface. The client exception mapper allows developers to process a REST Response
into a Throwable
prior to the error being delivered to the ErrorCallback
described above. The exception mapper class must be annotated with javax.ws.rs.ext.Provider
as well as implement the ClientExceptionMapper
interface.
@Provider
public class MyAppExceptionMapper implements ClientExceptionMapper {
/**
* @see org.jboss.errai.enterprise.client.jaxrs.ClientExceptionMapper#fromResponse(com.google.gwt.http.client.Response)
*/
@Override
public Throwable fromResponse(Response response) {
if (response.getStatusCode() == 404)
return new MyAppNotFoundException();
else
return new MyAppServerError(response.getStatusText());
}
}
It is important to note that the ClientExceptionMapper
will only be invoked when the callback passed to the Caller
is an instance of RestErrorCallback
.
The ClientExceptionMapper
will, by default, be invoked for every error response. However, Errai also provides the org.jboss.errai.enterprise.shared.api.annotations.MapsFrom
annotation which provides for additional granularity. An exception mapper can be annotated so that it is only invoked for methods on specific REST interfaces.
@Provider
@MapsFrom({ SomeRestInterface.class })
public class SpecificClientExceptionMapper implements ClientExceptionMapper {
/**
* @see org.jboss.errai.enterprise.client.jaxrs.ClientExceptionMapper#fromResponse(com.google.gwt.http.client.Response)
*/
@Override
public Throwable fromResponse(Response response) {
... // Do something specific here
}
}
Client-side remote call interceptors provide the ability to manipulate or bypass the request before it’s being sent. This is useful for implementing crosscutting concerns like caching or security features e.g:
To have a JAX-RS remote call intercepted, either an interface method or the JAX-RS implementation class method has to be annotated with @InterceptedCall
. If the type is annotated, all interface methods will be intercepted.
@Path("customers")
public interface CustomerService {
@GET
@Path("/{id}")
@Produces("application/json")
@InterceptedCall(MyCacheInterceptor.class)
public Customer retrieveCustomerById(@PathParam("id") long id);
}
Note that an ordered list of interceptors can be used for specifying an interceptor chain e.g.
@InterceptedCall({MyCacheInterceptor.class, MySecurityInterceptor.class})
public Customer retrieveCustomerById(@PathParam("id") long id);
Implementing an interceptor is easy:
public class MyCacheInterceptor implements RestClientInterceptor {
@Override
public void aroundInvoke(final RestCallContext context) {
RequestBuilder builder = context.getRequestBuilder();
builder.setHeader("headerName", "value");
context.proceed();
}
}
The RestCallContext
passed to the aroundInvoke
method provides access to the context of the intercepted JAX-RS (REST) remote call. It allows to read and write the parameter values provided at the call site and provides read/write access to the RequestBuilder
instance which has the URL, HTTP headers and parameters set.
Calling proceed
executes the next interceptor in the chain or the actual remote call if all interceptors have already been executed. If access to the result of the (asynchronous) remote call is needed in the interceptor, one of the overloaded versions of proceed
accepting a RemoteCallback
has to be used instead.
The result of the remote call can be manipulated by calling RestCallContext.setResult()
.
Not calling proceed
in the interceptor bypasses the actual remote call, passing RestCallContext.getResult()
to the RemoteCallBack
provided at the call site.
If you cannot (or do not wish to) annotate the JAX-RS interface you may instead define remote call interceptors by annotating the interceptor class itself with @InterceptsRemoteCall
. This annotation requires the developer to specify the JAX-RS interface that should be intercepted. The interceptor will then be applied to all methods in that interface. If the interface method is annotated with InterceptedCall
, that annotation will win out.
@InterceptsRemoteCall({ MyJaxrsInterface.class, MyOtherJaxrsInterface.class })
public class MyCacheInterceptor implements RestClientInterceptor {
@Override
public void aroundInvoke(final RestCallContext context) {
// Do interceptor logic here
context.proceed();
}
}
This approach sacrifices granularity (you cannot intercept individual methods on the JAX-RS interface). However, it does allow method interception without modification to the JAX-RS interface (which is particularly useful when the developer is not in control of the JAX-RS interface).
It is worth noting that interceptors may be defined as managed beans using the @Dependent
, @Singleton
, or @ApplicationScoped
annotations. If the Errai application is using IOC (i.e. imports the IOC Errai module) and the interceptor is annotated as a managed bean, then the IOC container will be used to get/create the interceptor instance. This allows developers to @Inject
dependencies into interceptors. If IOC is not being used, or else the interceptor is not properly annotated, then the interceptor class will simply be instantiated via new.
Errai’s JSON format will be used to serialize/deserialize your custom types. See Marshalling for details.
Alternatively, a Jackson compatible JSON format can be used on the wire. See Configuration for details on how to enable Jackson marshalling.
All paths specified using the @Path
annotation on JAX-RS interfaces are by definition relative paths. Therefore, by default, it is assumed that the JAX-RS endpoints can be found at the specified paths relative to the GWT client application’s context path.
To learn more about configuring the path, checkout the JAX-RS Configuration Section.
Starting with Errai 2.1, Errai implements a subset of JPA 2.0. With Errai JPA, you can store and retrieve entity objects on the client side, in the browser’s local storage. This allows the reuse of JPA-related code (both entity class definitions and procedural logic that uses the EntityManager) between client and server.
Errai JPA implements the following subset of JPA 2.0:
WHERE
clauseORDER BY
clauseMetamodel
, EntityType
, SingularAttribute
, PluralAttribute
, etc.)Errai JPA is a declarative, typesafe interface to the web browser’s localStorage
object. As such it is a client-side implementation of JPA. Objects are stored and fetched from the browser’s local storage, not from the JPA provider on the server side.
Use the Errai Forge Addon Add Errai Features command and select Errai JPA to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai JPA to your project.
Errai ignores META-INF/persistence.xml for purposes of client-side JPA. Instead, Errai scans all Java packages that are part of your GWT modules for classes annotated with @Entity
. This allows you the freedom of defining a persistence.xml that includes both shared entity classes that you use on the client and the server, plus server-only entities that are defined in a server-only package.
Classes whose instances can be stored and retrieved by JPA are called entities . To declare a class as a JPA entity, annotate it with @Entity
.
JPA requires that entity classes conform to a set of rules. These are:
Here is an example of a valid entity class with an ID attribute ( id
) and a String-valued persistent attribute ( name
):
@Entity
public class Genre {
@Id @GeneratedValue
private int id;
private String name;
// This constructor is used by JPA
public Genre() {}
// This constructor is not used by JPA
public Genre(String name) {
this();
this.name = name;
}
// These getter and Setter methods are optional:
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
}
The state of fields and JavaBeans properties of entities are generally persisted with the entity instance. These persistent things are called attributes .
JPA Attributes are subdivided into two main types: singular and plural . Singular attributes are scalar types like Integer
or String
. Plural attributes are collection values, such as List<Integer>
or Set<String>
.
The values of singular attributes (and the elements of plural attributes) can be of any application-defined entity type or a JPA Basic type. The JPA basic types are all of the Java primitive types, all boxed primitives, enums, BigInteger, BigDecimal, String, Date ( java.util.Date
or java.sql.Date
), Time, and Timestamp.
You can direct JPA to read and write your entity’s attributes by direct field access or via JavaBeans property access methods (that is, "getters and setters"). Direct field access is the default. To request property access, annotate the class with @Access(AccessType.PROPERTY)
. If using direct field access, attribute-specific JPA annotations should be on the fields themselves; when using property access, the attribute-specific annotations should be on the getter method for that property.
Each entity class must have exactly one ID attribute. The value of this attribute together with the fully-qualified class name uniquely identifies an instance to the entity manager.
ID values can be assigned by the application, or they can be generated by the JPA entity manager. To declare a generated identifier, annotate the field with @GeneratedValue
. To declare an application-assigned identifier, leave off the @GeneratedValue
annotation.
Generated identifier fields must not be initialized or modified by application code. Application-assigned identifier fields must be initialized to a unique value before the entity is persisted by the entity manager, but must not be modified afterward.
By default, every field of a JPA basic type is a persistent attribute. If a basic type field should not be presistent, mark it with transient
or annotate it with @Transient
.
Single-valued attributes of entity types must be annotated with @OneToOne
or @ManyToOne
.
Single-valued types that are neither entity types nor JPA Basic types are not presently supported by Errai JPA. Such attributes must be marked transient.
Here is an example of an entity with single-valued basic attributes and a single-valued relation to another entity type:
@Entity
public class Album {
@GeneratedValue
@Id
private Long id;
private String name;
@ManyToOne
private Artist artist;
private Date releaseDate;
private Format format;
public Long getId() { return id; }
public void setId(Long id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public Artist getArtist() { return artist; }
public void setArtist(Artist artist) { this.artist = artist; }
public Date getReleaseDate() { return releaseDate; }
public void setReleaseDate(Date releaseDate) { this.releaseDate = releaseDate; }
public Format getFormat() { return format; }
public void setFormat(Format format) { this.format = format; }
}
Collection-valued types Collection<T>
, Set<T>
, and List<T>
are supported. JPA rules require that all access to the collections are done through the collection interface method; never by specific methods on an implementation.
The element type of a collection attribute can be a JPA basic type or an entity type. If it is an entity type, the attribute must be annotated with @OneToMany
or @ManyToMany
.
Here is an example of an entity with two plural attributes:
@Entity
public class Artist {
@Id
private Long id;
private String name;
// a two-way relationship (albums refer back to artists)
@OneToMany(mappedBy="artist", cascade=CascadeType.ALL)
private Set<Album> albums = new HashSet<Album>();
// a one-way relationship (genres don't reference artists)
@OneToMany(cascade={CascadeType.PERSIST, CascadeType.MERGE})
private Set<Genre> genres = new HashSet<Genre>();
public Long getId() { return id; }
public void setId(Long id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public Set<Album> getAlbums() { return albums; }
public void setAlbums(Set<Album> albums) { this.albums = albums; }
public Set<Genre> getGenres() { return genres; }
public void setGenres(Set<Genre> genres) { this.genres = genres; }
}
When an entity changes state (more on this later), that state change can be cascaded automatically to related entity instances. By default, no state changes are cascaded to related entities. To request cascading of entity state changes, use the cascade
attribute on any of the relationship quantifiers @OneToOne
, @ManyToOne
, @OneToMany
, and @ManyToMany
.
CascadeType value | Description |
---|---|
| Persist the related entity object(s) when this entity is persisted |
| Merge the attributes of the related entity object(s) when this entity is merged |
| Remove the related entity object(s) from persistent storage when this one is removed |
| Not applicable in Errai JPA |
| Detach the related entity object(s) from the entity manager when this object is detached |
| Equivalent to specifying all of the above |
For an example of specifying cascade rules, refer to the Artist
example above. In that example, the cascade type on albums
is ALL
. When a particular Artist
is persisted or removed, detached, etc., all of that artist’s albums will also be persisted or removed, or detached correspondingly. However, the cascade rules for genres
are different: we only specify PERSIST
and MERGE
. Because a Genre
instance is reusable and potentially shared between many artists, we do not want to remove or detach these when one artist that references them is removed or detached. However, we still want the convenience of automatic cascading persistence in case we persist an Artist
which references a new, unmanaged Genre
.
The entity manager provides the means for storing, retrieving, removing, and otherwise affecting the lifecycle state of entity instances.
To obtain an instance of EntityManager on the client side, use Errai IoC (or CDI) to inject it into any client-side bean:
@EntryPoint
public class Main {
@Inject EntityManager em;
}
To store an entity object in persistent storage, pass that object to the EntityManager.persist()
method. Once this is done, the entity instance transitions from the new state to the managed state.
If the entity references any related entities, these entities must be in the managed state already, or have cascade-on-persist enabled. If neither of these criteria are met, an IllegalStateException
will be thrown.
See an example in the following section.
If you know the unique ID of an entity object, you can use the EntityManager.find()
method to retrieve it from persistent storage. The object returned from the find()
method will be in the managed state.
Example:
// make it
Album album = new Album();
album.setArtist(null);
album.setName("Abbey Road");
album.setReleaseDate(new Date(-8366400000L));
// store it
EntityManager em = getEntityManager();
em.persist(album);
em.flush();
em.detach(album);
assertNotNull(album.getId());
// fetch it
Album fetchedAlbum = em.find(Album.class, album.getId());
assertNotSame(album, fetchedAlbum);
assertEquals(album.toString(), fetchedAlbum.toString());
To remove a persistent managed entity, pass it to the EntityManager.remove()
method. As the cascade rules specify, related entities will also be removed recursively.
Once an entity has been removed and the entity manager’s state has been flushed, the entity object is unmanaged and back in the new state.
Errai’s EntityManager class provides a removeAll()
method which removes everything from the browser’s persistent store for the domain of the current webpage.
This method is not part of the JPA standard, so you must down-cast your client-side EntityManager
instance to ErraiEntityManager
. Example:
@EntryPoint
public class Main {
@Inject EntityManager em;
void resetJpaStorage() {
((ErraiEntityManager) em).removeAll();
}
}
For every entity instance in the managed state, changes to the attribute values of that entity are persisted to local storage whenever the entity manager is flushed. To prevent this automatic updating from happening, you can detach an entity from the entity manager. When an instance is detached, it is not deleted. All information about it remains in persistent storage. The next time that entity is retrieved, the entity manager will create a new and separate managed instance for it.
To detach one particular object along with all related objects whose cascade rules say so, call EntityManager.detach()
and pass in that object.
To detach all objects from the entity manager at once, call EntityManager.detachAll()
.
To retrieve one or more entities that match a set of criteria, Errai JPA allows the use of JPA named queries . Named queries are declared in annotations on entity classes.
Queries in JPA are written in the JPQL language. As of Errai 2.1, Errai JPA does not support all JPQL features. Most importantly, implicit and explicit joins in queries are not yet supported. Queries of the following form generally work:
SELECT et FROM EntityType et WHERE [expression with constants, named parameters and attributes of et] ORDER BY et.attr1 [ASC|DESC], et.attr2 [ASC|DESC]
Here is how to declare a JPQL query on an entity:
@NamedQuery(name="selectAlbumByName", query="SELECT a FROM Album a WHERE a.name=:name")
@Entity
public class Album {
... same as before ...
}
To declare more than one query on the same entity, wrap the @NamedQuery
annotations in @NamedQueries
like this:
@NamedQueries({
@NamedQuery(name="selectAlbumByName", query="SELECT a FROM Album a WHERE a.name = :name"),
@NamedQuery(name="selectAlbumsAfter", query="SELECT a FROM Album a WHERE a.releaseDate >= :startDate")
})
@Entity
public class Album {
... same as before ...
}
To execute a named query, retrieve it by name and result type from the entity manager, set the values of its parameters (if any), and then call one of the execution methods getSingleResult()
or getResultList()
.
Example:
TypedQuery<Album> q = em.createNamedQuery("selectAlbumByName", Album.class);
q.setParameter("name", "Let It Be");
List<Album> fetchedAlbums = q.getResultList();
To receive a notification when an entity instance transitions from one lifecycle state to another, use an entity lifecycle listener.
These annotations can be applied to methods in order to receive notifications at certain points in an entity’s lifecycle. These events are delivered for direct operations initiated on the EntityManager as well as operations that happen due to cascade rules.
Annotation | Meaning |
---|---|
| The entity is about to be persisted or merged into the entity manager. |
| The entity has just been persisted or merged into the entity manager. |
| The entity’s state is about to be captured into the browser’s localStorage. |
| The entity’s state has just been captured into the browser’s localStorage. |
| The entity is about to be removed from persistent storage. |
| The entity has just been removed from persistent storage. |
| The entity’s state has just been retrieved from the browser’s localStorage. |
JPA lifecycle event annotations can be placed on methods in the entity type itself, or on a method of any type with a public no-args constructor.
To receive lifecycle event notifications directly on the affected entity instance, create a no-args method on the entity class and annotate it with one or more of the lifecycle annotations in the above table.
For example, here is a variant of the Album class where instances receive notification right after they are loaded from persistent storage:
@Entity
public class Album {
... same as before ...
@PostLoad
public void postLoad() {
System.out.println("Album " + getName() + " was just loaded into the entity manager");
}
}
To receive lifecycle methods in a different class, declare a method that takes one parameter of the entity type and annotate it with the desired lifecycle annotations. Then name that class in the @EntityListeners
annotation on the entity type.
The following example produces the same results as the previous example:
@Entity
@EntityListeners(StandaloneLifecycleListener.class)
public class Album {
... same as always ...
}
public class StandaloneLifecycleListener {
@PostLoad
public void albumLoaded(Album a) {
public void postLoad() {
System.out.println("Album " + a.getName() + " was just loaded into the entity manager");
}
}
Errai captures structural information about entity types at compile time and makes them available in the GWT runtime environment. The JPA metamodel includes methods for enumerating all known entity types and enumerating the singular and plural attributes of those types. Errai extends the JPA 2.0 Metamodel by providing methods that can create new instances of entity classes, and read and write attribute values of existing entity instances.
As an example of what is possible, this functionality could be used to create a reusable UI widget that can present an editable table of any JPA entity type.
To access the JPA Metamodel, call the EntityManager.getMetamodel()
method. For details on what can be done with the stock JPA metamodel, see the API’s javadoc or consult the JPA specification.
Wherever you obtain an instance of SingularAttribute
from the metamodel API, you can down-cast it to ErraiSingularAttribute
. Likewise, you can down-cast any PluralAttribute
to ErraiPluralAttribute
.
In either case, you can read the value of an arbitrary attribute by calling ErraiAttribute.get()
and passing in the entity instance. You can set any attribute’s value by calling ErraiAttribute.set()
, passing in the entity instance and the new value.
In addition to get()
and set()
, ErraiPluralAttribute
also has the createEmptyCollection()
method, which creates an empty collection of the correct interface type for the given attribute.
The following features are not yet implemented, but could conceivably be implemented in a future Errai JPA release:
a.b.c
) do not yet work, although single-step attribute paths ( a.b
) do.SELECT
clause must specify exactly one entity type. Selection of individual attributes is not yet implemented.EntityManager.refresh()
to pick up changes made in localStorage from a different browser window/tab.@PersistenceContext
annotation currently has no effect in client-side code (use @Inject
instead)The following may never be implemented due to limitations and restrictions in the GWT client-side environment:
EntityManager.createQuery(String, …)
(that is, unnamed queries) are impractical because JPQL queries are parsed at compile time, not in the browser.EntityManager.createNativeQuery(String, …)
don’t make sense because the underlying database is just a hash table. It does not have a query language.java.util.Calendar
because the Calendar
class is not in GWT’s JRE emulation library.Traditional JPA implementations allow you to store and retrieve entity objects on the server side. Errai’s JPA implementation allows you to store and retrieve entity objects in the web browser using the same APIs. All that’s missing is the ability to synchronize the stored data between the server side and the client side.
This is where Errai JPA Data Sync comes in: it provides an easy mechanism for two-way synchronization of data sets between the client and the server.
Use the Errai Forge Addon Add Errai Features command and select Errai JPA Datasync to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai JPA Datasync to your project.
For the rest of this chapter, we will refer to the following Entity classes, which are defined in a shared
package that’s visible to client and server code:
@Portable
@Entity
@NamedQuery(name = "allUsers", query = "SELECT u FROM User u")
public class User {
@Id
@GeneratedValue
private long id;
private String name;
// getters and setters omitted
}
@Portable
@Entity
@NamedQuery(name = "groceryListsForUser", query = "SELECT gl FROM GroceryList gl WHERE gl.owner=:user")
public class GroceryList {
@Id
@GeneratedValue
private long id;
@ManyToOne
private User owner;
@OneToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH })
private List<Item> items = new ArrayList<Item>();
// getters and setters omitted
}
@Portable
@Entity
@NamedQuery(name = "allItems", query = "SELECT i FROM Item i")
public class Item {
@Id
@GeneratedValue
private long id;
private String name;
private String department;
private String comment;
private Date addedOn;
@ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH })
private User addedBy;
// getters and setters omitted
}
To summarize: there are three entity types: User
, GroceryList
, and Item
. Each GroceryList
belongs to a User
and has a list of Item
objects.
All the entities involved in the data synchronization request must be marshallable via Errai Marshalling. This is normally accomplished by adding the @Portable
annotation to each JPA entity class, but it is also acceptable to list them in ErraiApp.properties
. See the Marshalling section for more details.
Now let’s say we want to synchronize the data for all of a user’s grocery lists. This will make them available for offline use through Errai JPA, and at the same time it will update the server with the latest changes made on the client. Ultimately, the sync operation is accomplished via an annotated method or an asynchronous call into ClientSyncManager
, but first we have to prepare a few things on the client and the server.
A data sync operation begins when the client-side sync manager sends an Errai RPC request to the server. Although a server-side implementation of the remote interface is provided, you are responsible for implementing a thin wrapper around it. This wrapper serves two purposes:
If you are deploying to a container that supports CDI and EJB 3, you can use this DataSyncServiceImpl as a template for your own:
@Stateless @org.jboss.errai.bus.server.annotations.Service
public class DataSyncServiceImpl implements DataSyncService {
@PersistenceContext
private EntityManager em;
private final JpaAttributeAccessor attributeAccessor = new JavaReflectionAttributeAccessor();
@Inject private LoginService loginService;
@Override
public <X> List<SyncResponse<X>> coldSync(SyncableDataSet<X> dataSet, List<SyncRequestOperation<X>> remoteResults) {
// Ensure a user is logged in
User currentUser = loginService.whoAmI();
if (currentUser == null) {
throw new IllegalStateException("Nobody is logged in!");
}
// Ensure user is accessing their own data!
if (dataSet.getQueryName().equals("groceryListsForUser")) {
User requestedUser = (User) dataSet.getParameters().get("user");
if (!currentUser.getId().equals(requestedUser.getId())) {
throw new AccessDeniedException("You don't have permission to sync user " + requestedUser.getId());
}
}
else {
throw new IllegalArgumentException("You don't have permission to sync dataset " + dataSet.getQueryName());
}
DataSyncService dss = new org.jboss.errai.jpa.sync.server.DataSyncServiceImpl(em, attributeAccessor);
return dss.coldSync(dataSet, remoteResults);
}
}
If you are not using EJB 3, you will not be able to use the @PersistenceContext
annotation. In this case, obtain a reference to your EntityManager the same way you would anywhere else in your application.
Like many Errai features, Errai JPA DataSync provides an annotation-driven programming model and a programmatic API. You can choose which to use based on your needs and preferences.
The declarative data sync API is driven by the @Sync
annotation. Consider the following example client-side class:
// This injected User object could have been set up in a @PostConstruct method instead of being injected.
@Inject
private User syncThisUser;
@Sync(query = "groceryListsForUser", params = { @SyncParam(name = "user", val = "{syncThisUser}") })
private void onDataSyncComplete(SyncResponses<GroceryList> responses) {
Window.alert("Data Sync Complete!");
}
By placing the above code snippet in a client-side bean, you tell Errai JPA Data Sync that, as long as a managed
instance of the bean containing the @Sync
method exists, the Data Sync system should keep all grocery lists
belonging to the syncThisUser
user in sync between the client-side JPA EntityManager and the server-side EntityManager.
Right now, the data sets are kept in sync using a sync request every 5 seconds. In the future, this may be optimised
to an incremental approach that pushes changes as they occur.
The annotated method needs to have exactly one parameter of type SyncResponses
and will
be called each time a data sync operation has completed. All sync operations passed to the
method will have already been applied to the local EntityManager, with conflicts resolved in
favour of the server’s version of the data. The original client values are available in the
SyncResponses
object, which gives you a chance to implement a different conflict
resolution policy.
The query
attribute on the @Sync
annotation must refer to an existing JPA Named Query that is defined on a shared
JPA entity class.
The params
attribute is an array of @SyncParam
annotations. There must be exactly one @SyncParam
for each named
parameter in the JPA query (positional parameters are not supported). If the val
argument is surrounded with brace
brackets (as it is in the example aboce) then it is interpreted as a reference to a declared or inherited field in
the containing class. Otherwise, it is interpreted as a literal String value.
Field-reference sync params are captured just after the bean’s @PostConstruct
method is invoked. This means that
values of referenced fields can be provided using @Inject
(which in turn could come from a CDI Producer method)
or by code in the @PostConstruct
method.
Transport (network) errors are logged to the slf4j logger channel org.jboss.errai.jpa.sync.client.local.ClientSyncWorker
.
As of Errai 3.0.0.M4, it is not possible to specify a custom error handler using the declarative API. See the next
section for information about the programmatic API.
@Inject private ClientSyncManager syncManager;
@Inject private EntityManager em;
public void syncGroceryLists(User forUser) {
RemoteCallback<List<SyncResponse<GroceryList>>> onCompletion = new RemoteCallback<List<SyncResponse<GroceryList>>>() {
@Override
public void callback(List<SyncResponse<GroceryList>> response) {
Window.alert("Data Sync Complete!");
}
};
ErrorCallback<?> onError = new BusErrorCallback() {
@Override
public boolean error(Message message, Throwable throwable) {
Window.alert("Data Sync failed!");
return false;
}
};
Map<String, Object> queryParams = new HashMap<String, Object>();
queryParams.put("user", forUser);
syncManager.coldSync("groceryListsForUser", GroceryList.class, queryParams, onCompletion, onError);
}
The onCompletion
and onError
callbacks are optional. In the unlikely case that your application doesn’t
care if a data sync request completed successfully, you can pass null
for either callback.
Once your onCompletion
callback has been notified, the server and client will have the same entities stored in
their respective databases for all entities reachable from the given query result.
When the client sends the sync request to the server, it includes information about the state it expects each entity to be in. If an entity’s state on the server does not match this expected state on the client, the server ignores the client’s change request and includes a ConflictResponse
object in the sync reply.
When the client processes the sync responses from the server, it applies the new state from the server to the local data store. This overwrites the change that was initially requested from the client. In short, you could call this the "server wins" conflict resolution policy.
In some cases, your application may be able to do something smarter: apply domain-specific knowledge to merge the conflict automatically, or prompt the user to perform a manual merge. In order to do this, you will have to examine the server response from inside the onCompletion
callback you provided to the coldSync()
method:
RemoteCallback<List<SyncResponse<GroceryList>>> onCompletion = new RemoteCallback<List<SyncResponse<GroceryList>>>() {
@Override
public void callback(List<SyncResponse<GroceryList>> responses) {
for (SyncResponse<GroceryList> response : responses) {
if (response instanceof ConflictResponse) {
ConflictResponse<GroceryList> cr = (ConflictResponse<GroceryList>) response;
List<Item> expectedItems = cr.getExpected().getItems();
List<Item> serverItems = cr.getActualNew().getItems();
List<Item> clientItems = cr.getRequestedNew().getItems();
// merge the list of items by comparing each to expectedItems
List<Item> merged = ...;
// update local storage with the merged list
em.find(GroceryList.class, cr.getActualNew().getId()).setItems(merged);
em.flush();
}
}
}
};
Remember, because of Errai’s default "server wins" resolution policy, the call to em.find(GroceryList.class, cr.getActualNew().getId())
will return a GroceryList object that has already been updated to match the state present in serverItems
.
Searching for ConflictResponse objects in the onCompletion
callback is the only way to recover client data that was clobbered in a conflict. If you do not merge this data back into local storage, or at least retain a reference to the cr.getRequestedNew()
object, this conflicting client data will be lost forever.
In a future release of Errai JPA, we plan to provide a client-side callback mechanism for custom conflict handling. If such a callback is registered, it will override the default behaviour.
Errai’s data binding module provides the ability to bind model objects to UI fields/widgets. The bound properties of the model and the UI components will automatically be kept in sync for as long as they are bound. So, there is no need to write code for UI updates in response to model changes and no need to register listeners to update the model in response to UI changes.
The data binding module is directly integrated with Errai UI and Errai JPA but can also be used as a standalone project in any GWT client application:
Use the Errai Forge Addon Add Errai Features command and select Errai Data Binding to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai Data Binding to your project.
Objects that should participate in data bindings have to be marked as @Bindable
and must follow Java bean conventions. All editable properties of these objects are then bindable to UI widgets.
Example 9.1. Customer.java
@Bindable
public class Customer {
...
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
...
}
If you cannot or prefer not to annotate your classes with @Bindable
, you can alternatively specify bindable types in your ErraiApp.properties using a whitespace-separated list of fully qualified class names: errai.ui.bindableTypes=org.example.Model1 org.example.Model2
An instance of DataBinder
is required to create bindings. It can either be
injected into a client-side bean:
public class CustomerView {
@Inject
private DataBinder<Customer> dataBinder;
}
or created manually:
DataBinder<Customer> dataBinder = DataBinder.forType(Customer.class);
In both cases above, the DataBinder
instance is associated with a new instance of the model (e.g. a new Customer
object). A DataBinder
can also be associated with an already existing object:
DataBinder<Customer> dataBinder = DataBinder.forModel(existingCustomerObject);
In case there is existing state in either the model object or the UI components before the they are bound, initial state synchronization can be carried out to align the model and the corresponding UI fields.
For using the model object’s state to set the initial values in the UI:
DataBinder<Customer> dataBinder = DataBinder.forModel(existingCustomerObject, InitialState.FROM_MODEL);
For using the UI values to set the initial state in the model object:
DataBinder<Customer> dataBinder = DataBinder.forModel(existingCustomerObject, InitialState.FROM_UI);
Bindings can be created by calling the bind
method on a DataBinder
instance, thereby specifying which widgets should be bound to which properties of the model. It is possible to use property chains for bindings, given that all nested properties are of bindable types. When binding to customer.address.streetName
, for example, both customer
and address
have to be of a type annotated with @Bindable
.
public class CustomerView {
@Inject
private DataBinder<Customer> dataBinder;
private Customer customer;
private TextBox nameTextBox = new TextBox();
// more UI widgets...
@PostConstruct
private void init() {
customer = dataBinder
.bind(nameTextBox, "name")
.bind(idLabel, "id")
.getModel();
}
}
After the call to dataBinder.bind()
in the example above, the customer object’s name property and the nameTextBox
are kept in sync until either the dataBinder.unbind()
method is called or the CustomerView
bean is destroyed.
That means that a call to customer.setName()
will automatically update the value of the TextBox and any change to the TextBox’s value in the browser will update the customer object’s name property. So, customer.getName()
will always reflect the currently displayed value of the TextBox
.
It’s important to retrieve the model instance using dataBinder.getModel() before making changes to it as the data binder will provide a proxy to the model to ensure that changes will update the corresponding UI components.
Errai also provides a declarative binding API that can be used to create bindings automatically based on matching field and model property names.
Errai has built-in conversion support for all Number types as well as Boolean and Date to java.lang.String and vice versa. However, in some cases it will be necessary to provide custom converters (e.g. if a custom date format is desired). This can be done on two levels.
@DefaultConverter
public class MyCustomDateConverter implements Converter<Date, String> {
private static final String DATE_FORMAT = "YY_DD_MM";
@Override
public Date toModelValue(String widgetValue) {
return DateTimeFormat.getFormat(DATE_FORMAT).parse(widgetValue);
}
@Override
public String toWidgetValue(Date modelValue) {
return DateTimeFormat.getFormat(DATE_FORMAT).format((Date) modelValue);
}
}
All converters annotated with @DefaultConverter
will be registered as global defaults calling Convert.registerDefaultConverter()
. Note that the Converter
interface specifies two type parameters. The first one represents the type of the model field, the second one the type held by the widget (e.g. String
for widgets implementing HasValue<String>
). These default converters will be used for all bindings with matching model and widget types.
In some cases keeping the model and the UI in sync is not enough. Errai’s DataBinder
allows for the registration of PropertyChangeHandlers
for specific properties, property expressions or all properties of a bound model. A property expression can be a property chain such as customer.address.street. It can end in a wildcard to indicate that changes of any property of the corresponding bean should be observed (e.g "customer.address.*"
). A double wildcard can be used at the end of a property expression to register a cascading change handler for any nested property (e.g "customer.\*\*"
).
This provides a uniform notification mechanism for model and UI value changes. PropertyChangeHandlers
can be used to carry out any additional logic that might be necessary after a model or UI value has changed.
dataBinder.addPropertyChangeHandler(new PropertyChangeHandler() {
@Override
public void onPropertyChange(PropertyChangeEvent event) {
Window.alert(event.getPropertyName() + " changed to:" + event.getNewValue());
}
});
dataBinder.addPropertyChangeHandler("name", new PropertyChangeHandler() {
@Override
public void onPropertyChange(PropertyChangeEvent event) {
Window.alert("name changed to:" + event.getNewValue());
}
});
Programmatic binding as described above (see Creating Bindings ) can be tedious when working with UI components that contain a large number of input fields. Errai provides an annotation-driven binding API that can be used to create bindings automatically which cuts a lot of boilerplate code. The declarative API will work in any Errai IOC managed bean (including Errai UI templates). Simply inject a data binder or model object and declare the bindings using @Bound
.
Here is a simple example using an injected model object provided by the @Model
annotation (field injection is used here, but constructor and method injection are supported as well):
@Dependent
public class CustomerView {
@Inject @Model
private Customer customer;
@Inject @Bound
private TextBox name;
@Bound
private Label id = new Label();
....
}
Here is the same example injecting a DataBinder
instead of the model object. This is useful when more control is needed (e.g. the ability to register property change handlers). The @AutoBound
annotation specifies that this DataBinder
should be used to bind the model to all enclosing widgets annotated with @Bound
. This example uses field injection again but constructor and method injection are supported as well.
@Dependent
public class CustomerView {
@Inject @AutoBound
private DataBinder<Customer> customerBinder;
@Inject @Bound
private TextBox name;
@Bound
private Label id = new Label();
...
}
In both examples above an instance of the Customer
model is automatically bound to the corresponding UI widgets based on matching field names. The model object and the UI fields will automatically be kept in sync. The widgets are inferred from all enclosing fields and methods annotated with @Bound
of the class that defines the @AutoBound DataBinder
or @Model
and all its super classes.
By default, bindings are determined by matching field names to property names on the model object. In the examples above, the field name
was automatically bound to the JavaBeans property name
of the model ( user
object). If the field name does not match the model property name, you can use the property
attribute of the @Bound
annotation to specify the name of the property. The property can be a simple name (for example, "name") or a property chain (for example, user.address.streetName
). When binding to a property chain, all properties but the last in the chain must refer to @Bindable values.
The following example illustrates all three scenarios:
@Bindable
public class Address {
private String line1;
private String line2;
private String city;
private String stateProv;
private String country;
// getters and setters
}
@Bindable
public class User {
private String name;
private String password;
private Date dob;
private Address address;
private List<Role> roles;
// getters and setters
}
@Templated
public class UserWidget {
@Inject @AutoBound DataBinder<User> user;
@Inject @Bound TextBox name;
@Inject @Bound("dob") DatePicker dateOfBirth;
@Inject @Bound("address.city") TextBox city;
}
In UserWidget
above, the name
text box is bound to user.name
using the default name matching; the dateOfBirth
date picker is bound to user.dob
using a simple property name mapping; finally, the city
text box is bound to user.address.city
using a property chain. Note that the Address
class is required to be @Bindable
in this case.
The @Bound
annotation further allows to specify a converter to use for the binding (see Specifying Converters for details). This is how a binding specific converter can be specified on a data field:
@Inject
@Bound(converter=MyDateConverter.class)
@DataField
private TextBox date;
The injected model objects in the examples above are always proxies to the actual model since method invocations on these objects need to trigger additional logic for updating the UI. Special care needs to be taken in case a model object should be replaced.
When working with an @AutoBound DataBinder
, simply calling setModel()
on the DataBinder
will be enough to replace the underlying model instance. However, when working with @Model
the instance cannot be replaced directly. Errai provides a special method level annotation @ModelSetter
that will allow replacing the model instance. Here’s an example:
@Dependent
public class CustomerView {
@Inject @Model
private Customer customer;
@Inject @Bound
private TextBox name;
@Bound
private Label id = new Label();
@ModelSetter
public void setModel(Customer customer) {
this.customer = customer;
}
}
The @ModelSetter
method is required to have a single parameter. The parameter type needs to correspond to the type of the managed model.
Java bean validation (JSR 303) provides a declarative programming model for validating entities. More details and examples can be found here . Errai provides a bean validation module that makes Validator
instances injectable and work well with Errai’s data binding module. The following line needs to be added to the GWT module descriptor to inherit Errai’s bean validation module:
Example 9.2. App.gwt.xml
<inherits name="org.jboss.errai.validation.Validation" />
<inherits name="org.hibernate.validator.HibernateValidator" />
To use Errai’s bean validation module, you must add the module, the javax.validation API and an implementation such as hibernate validator to your classpath. If you are using Maven for your build, add these dependencies:
<dependency>
<groupId>org.jboss.errai</groupId>
<artifactId>errai-validation</artifactId>
<version>${errai.version}</version>
</dependency>
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<classifier>sources</classifier>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
<version>4.2.0.Final</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
<version>4.2.0.Final</version>
<scope>provided</scope>
<classifier>sources</classifier>
</dependency>
Now it is as simple as injecting a Validator
instance into an Errai IOC managed bean and calling the validate
method.
@Inject
private Validator validator;
Set<ConstraintViolation<Customer>> violations = validator.validate(customer);
// display violations
By default, Errai scans the entire classpath for classes with constraints. But sometimes it is necessary or desirable to exclude some shared classes from being validated on the client side. This can be done by adding a list of classes and package masks to the ErraiApp.properties file like so:
# The following blacklists the class some.fully.qualified.ClassName and all classes in some.package.mask (and subpackages thereof). errai.validation.blacklist = some.fully.qualified.ClassName \ some.package.mask.*
One of the primary complaints of GWT to date has been that it is difficult to use "pure HTML" when building and skinning widgets. Inevitably one must turn to Java-based configuration in order to finish the job. Errai, however, strives to remove the need for Java styling. HTML template files are placed in the project source tree, and referenced from custom "Composite components" (Errai UI Widgets) in Java. Since Errai UI depends on Errai IOC and Errai CDI, dependency injection is supported in all custom components. Errai UI provides rapid prototyping and HTML5 templating for GWT.
The Errai UI module is directly integrated with Data Binding and Errai JPA but can also be used as a standalone project in any GWT client application by simply inheriting the Errai UI GWT module, and ensuring that you have properly using Errai CDI’s @Inject to instantiate your widgets:
Use the Errai Forge Addon Add Errai Features command and select Errai UI to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai UI to your project. If you work better by playing with a finished product, you can see a simple client-server project implemented using Errai UI here .
Before explaining how to create Errai UI components, it should be noted that these components behave no differently from any other GWT Widget once built. The primary difference is in A) their construction, and B) their instantiation. As with most other features of Errai, dependency injection with CDI is the programming model of choice, so when interacting with components defined using Errai UI, you should always @Inject
references to your Composite components.
@EntryPoint
public class Application {
@Inject
private ColorComponent comp;
@PostConstruct
public void init() {
comp.setColor("blue");
RootPanel.get().add(comp);
}
}
@EntryPoint
public class Application {
private String[] colors = new String[]{"Blue", "Yellow", "Red"};
@Inject
private Instance<ColorComponent> instance;
@PostConstruct
public void init() {
for(String color: colors) {
ColorComponent comp = instance.get();
comp.setColor(c);
RootPanel.get().add();
}
}
}
Custom components in Errai UI are single classes extending from com.google.gwt.user.client.ui.Composite
, and must be annotated with @Templated.
@Templated
public class LoginForm extends Composite {
/* looks for LoginForm.html in LoginForm's package */
}
With default values, @Templated informs Errai UI to look in the current package for a parallel ".html"
template next to the Composite component Class; however, the template name may be overridden by passing a String into the @Templated annotation, like so:
@Templated("my-template.html")
public class LoginForm extends Composite {
/* looks for my-template.html in LoginForm's package */
}
Fully qualified template paths are also supported, but must begin with a leading /:
@Templated("/org/example/my-template.html")
public class LoginForm extends Composite {
/* looks for my-template.html in package org.example */
}
Templates in Errai UI may be designed either as an HTML snippet or as a full HTML document. You can even take an existing HTML page and use it as a template. With either approach, the id
, class
, and data-field
attributes in the template identify elements by name. These elements and their children are used in the Composite component to add behavior, and use additional components to add functionality to the template. There is no limit to how many component classes may share a given HTML template.
We will begin by creating a simple HTML login form to accompany our @Templated LoginForm
composite component.
<form>
<legend>Log in to your account</legend>
<label for="username">Username</label>
<input id="username" type="text" placeholder="Username">
<label for="password">Password</label>
<input id="password" type="password" placeholder="Password">
<button>Log in</button>
<button>Cancel</button>
</form>
Or as a full HTML document which may be more easily previewed during design without running the application; however, in this case we must also specify the location of our component’s root DOM Element using a "data-field"
, id
, or class
attribute matching the value of the @Templated annotation. There is no limit to how many component classes may share a given HTML template.
@Templated("my-template.html#login-form")
public class LoginForm extends Composite {
/* Specifies that <... id="login-form"> be used as the root Element of this Widget */
}
Notice the corresponding HTML id
attribute in the form Element below (we could have used data-field
or class
instead). Note that multiple components may use the same template provided that they specify a corresponding data-field
, id
, or class
attribute. Also note that two or more components may share the same DOM elements; there is no conflict since components each receive a unique copy of the template DOM rooted at the designated element at runtime (or from the root element if a fragment is not specified.)
<!DOCTYPE html>
<html lang="en">
<head>
<title>A full HTML snippet</title>
</head>
<body>
<div>
<form id="login-form">
<legend>Log in to your account</legend>
<label for="username">Username</label>
<input id="username" type="text" placeholder="Username">
<label for="username">Password</label>
<input id="password" type="password" placeholder="Password">
<button>Log in</button>
<button>Cancel</button>
</form>
</div>
<hr>
<footer id="theme-footer">
<p>(c) Company 2012</p>
</footer>
</body>
</html>
For example’s sake, the component below could also use the same template. All it needs to do is reference the template name, and specify a fragment.
@Templated("my-template.html#theme-footer")
public class Footer extends Composite {
/* Specifies that <... id="theme-footer"> be used as the root Element of this Widget */
}
Now that we have created the @Templated Composite component and an HTML template, we can start wiring in functionality and behavior; this is done by annotating fields and methods to replace specific sub-elements of the template DOM with other Widgets. We can even replace portions of the template with other Errai UI Widgets!
In order to composite Widgets into the template DOM, you annotate fields in your @Templated Composite component with @DataField, and mark the HTML template Element with a correspondingly named data-field
, id
, or class
attribute. This informs Errai UI which element in the template the Widget should replace. All replacements happen while the @Templated Composite component is being constructed; thus, fields annotated with @DataField must either be {{@Inject}}ed or provide their own Widget or Element instances in field initializers.
@Templated
public class LoginForm extends Composite {
// This element must be initialized manually because Element is not @Inject-able*/
@DataField
private Element form = DOM.createForm();
// If not otherwise specified, the name to match in the HTML template defaults to the name of the field; in this case, the name would be "username"
@Inject
@DataField
private TextBox username;
// The name to reference in the template can also be specified manually
@Inject
@DataField("pass")
private PasswordTextBox password;
// We can also choose to instantiate our own Widgets. Injection is not required.
@DataField
private Button submit = new Button();
}
Note: Field, method, and constructor injection are all supported by @DataField.
Each @DataField reference in the Java class must match an element in the HTML template. The matching of Java references to HTML elements is performed as follows:
@DataField
annotation has a value argument, that is used as the reference name. For fields, the default reference name is the field name. Method and constructor parameters have no default name, so they must always specify a value.data-field=name
, the Java reference will point to this element. If there is more than one such element, the Java reference points to the first.id=name
, the Java reference will point to this element. If there is more than one such element, the Java reference points to the first.name
, the Java reference will point to this element. If there is more than one such element, the Java reference points to the first. For elements with more than one CSS style, each style name is considered individually. For example:
<div class="eat drink be-merry">
matches Java references named eat
, drink
, or be-merry
.
If more than one Java reference matches the same HTML element in the template, it is an error. For example, given a template containing the element <div class="eat drink be-merry">
, the following Java code is in error:
@Templated
public class ErroneousTemplate extends Composite {
@Inject @DataField
private Label eat;
@Inject @DataField
private Label drink;
}
because both fields eat
and drink
refer to the same HTML div
element.
So now we must ensure there are data-field
, id
, or class
attributes in the right places in our template HTML file. This, combined with the @DataField annotation in our Composite component allow Errai UI to determine where and what should be composited when creating component instances.
<form id="form">
<legend>Log in to your account</legend>
<label for="username">Username</label>
<input id="username" type="text" placeholder="Username">
<label for="password">Password</label>
<input data-field="pass" id="password" type="password" placeholder="Password">
<button id="submit">Log in</button>
<button>Cancel</button>
</form>
Now, when we run our application, we will be able to interact with these fields in our Widget.
Three things are merged or modified when Errai UI creates a new Composite component instance:
@DataField
[code]Widget
implements HasText
or HasHTML
@Templated
public class StyledComponent extends Composite {
@Inject
@DataField("field-1")
private Label div = new Label();
public StyledComponent() {
div.getElement().setAttribute("style", "position: fixed; top: 0; left: 0;");
this.getElement().setId("outer-id");
}
}
<form>
<span data-field="field-1" style="display:inline;"> This element will become a div </span>
</form>
This text will be ignored.
<form id="outer-id">
<div data-field="field-1" style="display:inline;"> This element will become a div </div>
</form>
But why does the output look the way it does? Some things happened that may be unsettling at first, but we find that once you understand why these things occur, you’ll find the mechanisms extremely powerful.
When styling your templates, you should keep in mind that all attributes defined in the template file will take precedence over any preset attributes in your Widgets. This "attribute merge" occurs only when the components are instantiated; subsequent changes to any attributes after Widget construction will function normally. In the example we defined a Composite component that applied several styles to a child Widget in its constructor, but we can see from the output that the styles from the template have overridden them. If styles must be applied in Java, instead of the template, @PostConstruct
or other methods should be favored over constructors to apply styles to fully-constructed Composite components.
Element composition, however, functions inversely from attribute merging, and the <span>
defined in our template was actually be replaced by the <div>
Label in our Composite component field. This does not, however, change the behavior of the attribute merge - the new <div>
was still be rendered inline, because we have specified this style in our template, and the template always wins in competition with attributes set programatically before composition occurs. In short, whatever is inside the @DataField
in your class will replace the children of the corresponding element in your template.
Additionally, because Label
implements both HasText
and HasHTML
(only one is required,) the contents of this <span> "field-1" Element in the template were preserved; however, this would not have been the case if the @DataField
specified for the element did not implement HasText
or HasHTML
. In short, if you wish to preserve text or HTML contents of an element in your template, you can do one of two things: do not composite that Element with a @DataField
reference, or ensure that the Widget being composited implements HasText
or HasHTML
.
Dealing with User and DOM Events is a reality in rich web development, and Errai UI provides several approaches for dealing with all types of browser events using its "quick handler" functionality. It is possible to handle:
It is not possible to handle Native DOM events on Widgets because GWT overrides native event handlers when Widgets are added to the DOM. You must programatically configure such handlers after the Widget has been added to the DOM.
Each of the three scenarios mentioned above use the same basic programming model for event handling: Errai UI wires methods annotated with @EventHandler("my-data-field")
( event handler methods ) to handle events on the corresponding @DataField("my-data-field")
in the same component. Event handler methods annotated with a bare @EventHandler
annotation (no annotation parameter) are wired to receive events on the @Templated component itself.
Probably the simplest and most common use-case, this approach handles GWT Event classes for Widgets that explicitly handle the given event type. If a Widget does not handle the Event type given in the @EventHandler
method’s signature, the application will fail to compile and appropriate errors will be displayed.
@Templated
public class WidgetHandlerComponent extends Composite {
@Inject
@DataField("b1")
private Button button;
@EventHandler("b1")
public void doSomethingC1(ClickEvent e) {
// do something
}
}
Errai UI also makes it possible to handle GWT events on native Elements which are specified as a @DataField
in the component class. This is useful when a full GWT Widget is not available for a given Element, or for GWT events that might not normally be available on a given Element type. This could occur, for instance, when clicking on a <div>
, which would normally not have the ability to receive the GWT ClickEvent
, and would otherwise require creating a custom DIV Widget to handle such an event.
@Templated
public class ElementHandlerComponent extends Composite {
@DataField("div-1")
private DivElement button = DOM.createDiv();
@EventHandler("div-1")
public void doSomethingC1(ClickEvent e) {
// do something
}
}
The last approach is handles the case where native DOM events must be handled, but no such GWT event handler exists for the given event type. Alternatively, it can also be used for situations where Elements in the template should receive events, but no handle to the Element the component class is necessary (aside from the event handling itself.) Native DOM events do not require a corresponding @DataField
be configured in the class; only the HTML data-field
, id
, or class
template attribute is required.
<div>
<a id="link" href="/page">this is a hyperlink</a>
<div data-field="div"> Some content </div>
</div>
The @SinkNative
annotation specifies (as a bit mask) which native events the method should handle; this sink behaves the same in Errai UI as it would with DOM.sinkEvents(Element e, int bits)
. Note that a @DataField
reference in the component class is optional.
Only one @EventHandler may be specified for a given template element when @SinkNative is used to handle native DOM events.
@Templated
public class QuickHandlerComponent extends Composite {
@DataField
private AnchorElement link = DOM.createAnchor().cast();
@EventHandler("link")
@SinkNative(Event.ONCLICK | Event.ONMOUSEOVER)
public void doSomething(Event e) {
// do something
}
@EventHandler("div")
@SinkNative(Event.ONMOUSEOVER)
public void doSomethingElse(Event e) {
// do something else
}
}
Using asynchronous Javascript calls often make realizing the benefits of modern browsers difficult when it comes to form submission. But there is now a base class in Errai UI for creating @Templated
form widgets that are perfect for tasks such as creating a login form.
Here is a sample @Templated
login form class. This form has:
username
text fieldpassword
field@Dependent
@Templated
public class LoginForm extends AbstractForm { //
@Inject
private Caller<AuthenticationService> authenticationServiceCaller;
@Inject
@DataField
private TextBox username;
@Inject
@DataField
private PasswordTextBox password;
@DataField
private final FormElement form = DOM.createForm(); //
@Inject
@DataField
private Button login; //
@Override
protected FormElement getFormElement() {
return form; //
}
@EventHandler("login")
private void loginClicked(ClickEvent event) {
authenticationServiceCaller.call(new RemoteCallback<User>() {
@Override
public void callback(User response) {
// Now that we're logged in, submit the form
submit(); //
}
}).login(username.getText(), password.getText());
}
}
The key things that you should take from this example:
The class extends | |
The | |
The login button is a regular button widget, with a click handling method below. | |
The | |
After the user has successfully logged in asynchronously we call |
When a user successfully logs in via this example, the web browser should prompt them to remember the username and password (assuming this is a feature of the browser being used).
The most likely way to go wrong is to accidentally use the wrong types of elements in your template. It is very important that you use a proper from
element with input
elements with the exception of the submit button. Here is an html template that could accompany the LoginForm.java
example above:
<div>
<form data-field="form">
<input type="text" name="username" data-field="username">
<input type="password" name="password" data-field="password">
<button data-field="login">Sign In</button>
</form>
</div>
To reiterate, notice that the username
and password
fields are legitimate input
elements. This is because we want these values to be submitted when AbstractForm.submit()
is called (so that the browser notices them). However, we do not want there to be any way to submit the form other than calling AbstractForm.submit()
, so the button
element is notably missing the type="submit"
attribute pair.
A recurring implementation task in rich web development is writing event handler code for updating model objects to reflect input field changes in the user interface. The requirement to update user interface fields in response to changed model values is just as common. These tasks require a significant amount of boilerplate code which can be alleviated by Errai. Errai’s data binding module provides the ability to bind model objects to user interface fields, so they will automatically be kept in sync. While the module can be used on its own, it can cut even more boilerplate when used together with Errai UI.
In the following example, all @DataFields
annotated with @Bound
have their contents bound to properties of the data model (a User
object). The model object is injected and annotated with @Model
, which indicates automatic binding should be carried out. Alternatively, the model object could be provided by an injected DataBinder
instance annotated with @AutoBound
, see Declarative Binding for details.
@Templated
public class LoginForm extends Composite {
@Inject
@Model
private User user;
@Inject
@Bound
@DataField
private TextBox name;
@Inject
@Bound
@DataField
private PasswordTextBox password;
@DataField
private Button submit = new Button();
}
Now the user object and the username
and password
fields in the UI are automatically kept in sync. No event handling code needs to be written to update the user object in response to input field changes and no code needs to be written to update the UI fields when the model object changes. So, with the above annotations in place, it will always be true that user.getUsername().equals(username.getText())
and user.getPassword().equals(password.getText())
.
By default, bindings are determined by matching field names to property names on the model object. In the example above, the field name
was automatically bound to the JavaBeans property name
of the model ( user
object). If the field name does not match the model property name, you can use the property
attribute of the @Bound
annotation to specify the name of the property. The property can be a simple name (for example, "name") or a property chain (for example, user.address.streetName
). When binding to a property chain, all properties but the last in the chain must refer to @Bindable values.
The following example illustrates all three scenarios:
@Bindable
public class Address {
private String line1;
private String line2;
private String city;
private String stateProv;
private String country;
// getters and setters
}
@Bindable
public class User {
private String name;
private String password;
private Date dob;
private Address address;
private List<Role> roles;
// getters and setters
}
@Templated
public class UserWidget extends Composite {
@Inject @AutoBound DataBinder<User> user;
@Inject @Bound TextBox name;
@Inject @Bound("dob") DatePicker dateOfBirth;
@Inject @Bound("address.city") TextBox city;
}
In UserWidget
above, the name
text box is bound to user.name
using the default name matching; the dateOfBirth
date picker is bound to user.dob
using a simple property name mapping; finally, the city
text box is bound to user.address.city
using a property chain. Note that the Address
class is required to be @Bindable
in this case.
Often you will need to bind a list of model objects so that every object in the list is bound to a corresponding widget. This task can be accomplished using Errai UI’s ListWidget
class. Here’s an example of binding a list of users using the UserWidget
class from the previous example. First, we need to enhance UserWidget
to implement HasModel
.
@Templated
public class UserWidget extends Composite implements HasModel<User> {
@Inject @AutoBound DataBinder<User> userBinder;
@Inject @Bound TextBox name;
@Inject @Bound("dob") DatePicker dateOfBirth;
@Inject @Bound("address.city") TextBox city;
public User getModel() {
userBinder.getModel();
}
public void setModel(User user) {
userBinder.setModel(user);
}
}
Now we can use UserWidget
to display items in a list.
@Templated
public class MyComposite extends Composite {
@Inject @DataField ListWidget<User, UserWidget> userListWidget;
@PostConstruct
public void init() {
List<User> users = .....
userListWidget.setItems(users);
}
}
Calling setItems
on the userListWidget
causes an instance of UserWidget
to be displayed for each user in the list. The UserWidget
is then bound to the corresponding user object. By default, the widgets are arranged in a vertical panel. However, ListWidget
can also be subclassed to provide alternative behaviour. In the following example, we use a horizontal panel to display the widgets.
public class UserListWidget extends ListWidget<User, UserWidget> {
public UserList() {
super(new HorizontalPanel());
}
@PostConstruct
public void init() {
List<User> users = .....
setItems(users);
}
@Override
public Class<UserWidget> getItemWidgetType() {
return UserWidget.class;
}
}
An instance of ListWidget
can also participate in automatic bindings using @Bound
. In this case, setItems
never needs to be called manually. The bound list property and displayed items will automatically be kept in sync. In the example below a list of user roles is bound to a ListWidget
that displays and manages a RoleWidget
for each role in the list. Every change to the list returned by user.getRoles()
will now trigger a corresponding update in the UI.
@Templated
public class UserDetailView extends Composite {
@Inject
@Bound
@DataField
private TextBox name;
@Inject
@Bound
@DataField
private PasswordTextBox password;
@Inject
@Bound
@DataField
private ListWidget<Role, RoleWidget> roles;
@DataField
private Button submit = new Button();
@Inject @Model
private User user;
}
The @Bound
annotation further allows to specify a converter to use for the binding (see Specifying Converters for details). This is how a binding specific converter can be specified on a data field:
@Inject
@Bound(converter=MyDateConverter.class)
@DataField
private TextBox date;
Errai’s DataBinder
also allows to register PropertyChangeHandlers
for the cases where keeping the model and UI in sync is not enough and additional logic needs to be executed (see Property Change Handlers for details).
Using Composite components to build up a hierarchy of widgets functions exactly the same as when building hierarchies of GWT widgets. The only distinction might be that with Errai UI, @Inject
is preferred to manual instantiation.
@Templated
public class ComponentOne extends Composite {
@Inject
@DataField("other-comp")
private ComponentTwo two;
}
Templating would not be complete without the ability to inherit from parent templates, and Errai UI also makes this possible using simple Java inheritance. The only additional requirement is that Composite components extending from a parent Composite component must also be annotated with @Templated, and the path to the template file must also be specified in the child component’s annotation. Child components may specify @DataField
references that were omitted in the parent class, and they may also override @DataField
references (by using the same data-field
name) that were already specified in the parent component.
Extension templating is particularly useful for creating reusable page layouts with some shared content (navigation menus, side-bars, footers, etc…,) where certain sections will be filled with unique content for each page that extends from the base template; this is commonly seen when combined with the MVP design pattern traditionally used in GWT applications.
<div class="container">
<div id="header"> Default header </div>
<div id="content"> Default content </div>
<div id="footer"> Default footer </div>
</div>
This component provides the common features of our page layout, including header and footer, but does not specify any content. The missing @DataField "content" will be provided by the individual page components extending from this parent component.
@Templated
public class PageLayout extends Composite {
@Inject
@DataField
private HeaderComponent header;
@Inject
@DataField
private FooterComponent footer;
@PostConstruct
public final void init() {
// do some setup
}
}
We are free to fill in the missing "content" @DataField with a Widget of our choosing. Note that it is not required to fill in all omitted @DataField references.
@Templated("PageLayout.html")
public class LoginLayout extends PageLayout {
@Inject
@DataField
private LoginForm content;
}
We could also have chosen to override one or more @DataField
references defined in the parent component, simply by specifying a @DataField
with the same name in the child component, as is done with the "footer" data field below.
@Templated("PageLayout.html")
public class LoginLayout extends PageLayout {
@Inject
@DataField
private LoginForm content;
/* Override footer defined in PageLayout */
@Inject
@DataField
private CustomFooter footer;
}
When developing moderately-complex web applications with Errai, you may find yourself needing to do quite a bit of programmatic style changes. One common case is showing or enabling controls only if a user has the necessary permissions to use them. One part of the problem is securing those features from being used, and the other part which is an important usability consideration is communicating that state to the user.
Errai Security contains a RestrictedAccess
annotation that uses style sheet binding to implement a feature similar in nature to this example.
Let’s start with the example case I just described. We have a control that we only want to be visible if the user is an admin. So the first thing we do is create a style binding annotation.
@StyleBinding
@Retention(RetentionPolicy.RUNTIME)
public @interface Admin {
}
This defines Admin
as a stylebinding now we can use it like this:
@EntryPoint
@Templated
public class HelloWorldForm extends Composite {
@Inject @Admin @DataField Button deleteButton;
@Inject SessionManager sessionManager;
@EventHandler("deleteButton")
private void handleSendClick(ClickEvent event) {
// do some deleting!
}
@Admin
private void applyAdminStyling(Style style) {
if (!sessionManager.isAdmin()) {
style.setVisibility(Style.Visibility.HIDDEN);
}
}
}
Now before the form is shown to the user the applyAdminStyling
method will be executed where the sessionManager
is queried to see if the user is an admin if not the delete button that is also annotated with @Admin
will be hidden from the view.
The above example took at Style
object as a parameter, but it is also possible to use an Element
. So the applyAdminStyling
method above could have also been written like this:
@Admin
private void applyAdminStyling(Element element) {
if (!sessionManager.isAdmin()) {
element.addClassName("disabled");
}
}
The CSS class "disabled" could apply the same style as before ("visibility: hidden") or it could have more complex behaviour that is dependent on the element type.
User interfaces often need to be available in multiple languages. To get started with Errai’s internationalization support, simply put the @Bundle("bundle.json")
annotation on your entry point and add an empty bundle.json
file to your classpath (e.g. to src/main/java or src/main/resources). Of course, you can name it differently.
Errai will scan your HTML templates and process all text elements to generate key/value pairs for translation. It will generate a file called errai-bundle-all.json
and put it in your .errai
directory. You can copy this generated file and use it as a starting point for your custom translation bundles. If the text value is longer than 128 characters the key will get cut off and a hash appended at the end.
The translation bundle files use the same naming scheme as Java (e.g. bundle_nl_BE.json
for Belgian Dutch and bundle_nl.json
for plain Dutch). Errai will also generate a file called errai-bundle-missing.json
in the .errai
folder containing all template values for which no translations have been defined. You can copy the key/value pairs out of this file to create our own translations:
{
"StoresPage.Stores!" : "Stores!",
"WelcomePage.As_you_move_toward_a_more_and_more_declarative_style,_you_allow_the_compiler_and_the_framework_to_catch_more_mistakes_up_front._-734987445" : "As you move toward a more and more declarative style, you allow the compiler and the framework to catch more mistakes up front. Broken links? A thing of the past!"
}
If you want to use your own keys instead of these generated ones you can specify them in your templates using the data-i18n-key
attribute:
<html>
<body>
<div id="content">
<p data-i18n-key="welcome">Welcome to errai-ui i18n.</p>
<div>
...
By adding this attribute in the template you can translate it with the following:
{
"Widget.welcome": "Willkommen bei Errai-ui i18n."
}
Because your templates are designer templates and can contain some mock data that doesn’t need to be translated, Errai has the ability to indicate that with an attribute data-role=dummy
:
<div id=navbar data-role=dummy>
<div class="navbar navbar-fixed-top">
<div class=navbar-inner>
<div class=container>
<span class=brand>Example Navbar</span>
<ul class=nav>
<li><a>Item</a>
<li><a>Item</a>
</ul>
</div>
</div>
</div>
</div>
Here the template fills out a navbar with dummy elements, useful for creating a design, adding data-role=dummy
will not only exclude it form being translated it will also strip the children nodes from the template that will be used by the application.
When you have setup a translation of your application Errai will look at the browser locale and select the locale, if it’s available, if not it will use the default ( bundle.json
). If the users of your application need to be able to switch the language manually, Errai offers a pre build component you can easily add to your page: LocaleListBox
will render a Listbox with all available languages. If you want more control of what this language selector looks like there is also a LocaleSelector
that you can use to query and select the locale for example:
@Templated
public class NavBar extends Composite {
@Inject
private LocaleSelector selector;
@Inject @DataField @OrderedList
ListWidget<Locale, LanguageItem> language;
@AfterInitialization
public void buildLangaugeList() {
language.setItems(new ArrayList<Locale>(selector.getSupportedLocales()));
}
...
// in LanguageItem we add a click handler on a link
@Inject
Navigation navigation;
@Inject
private LocaleSelector selector;
link.addClickHandler(new ClickHandler() {
@Override
public void onClick(ClickEvent event) {
selector.select(model.getLocale());
navigation.goTo(navigation.getCurrentPage().name());
}
});
Errai also supports LESS stylesheets. To get started using these you’ll have to create a LESS stylesheet and place it on the classpath of your project. Errai will convert the LESS stylesheet to css preform optimisations on it and ensure that is get injected into the pages of your application. It will also obfuscate the class selectors and replace the use of those in your templates. To be able to use the selectors in your code you can use:
public class MyComponent extends Component {
@Inject
private LessStyle lessStyle;
...
@PostCreate
private void init() {
textBox.setStyleName(lessStyle.get("input"));
}
}
Finally it will also add any deferred binding properties to the top of your LESS stylesheet, so for example you could use the user.agent in LESS like this:
.mixin (@a) when (@a = "safari") {
background-color: black;
}
.mixin (@a) when (@a = "gecko1_8") {
background-color: white;
}
.class1 { .mixin(@user_agent) }
Because a dot is not allowed in LESS variables it’s replaced with an underscore, so in the example above class1 will have a black background on Safari and Chrome and white on Firefox. On the top of this LESS stylesheet @user_agent: "safari" will get generated.
Starting in version 2.1, Errai offers a system for creating applications that have multiple bookmarkable pages. This navigation system has the following features:
Use the Errai Forge Addon Add Errai Features command and select Errai Navigation to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai Navigation to your project.
Errai Navigation has three main parts: the @Page
annotation marks any widget as a page; the TransitionTo<P>
interface is an injectable type that provides a link to another page; and the Navigation
singleton offers control over the navigation system as a whole.
The Navigation
singleton owns a GWT Panel called the navigation panel . This panel always contains a widget corresponding to the the fragment ID (the part after the # symbol) in the browser’s location bar. Whenever the fragment ID changes for any reason (for example, because the user pressed the back button, navigated to a bookmarked URL, or simply typed a fragment ID by hand), the widget in the navigation panel is replaced by the widget associated with that fragment ID. Likewise, when the application asks the navigation system to follow a link, the fragment ID in the browser’s location bar is updated to reflect the new current page.
To declare a page, annotate any subclass of Widget with the @Page
annotation:
@Page
public class ItemListPage extends Composite {
// Anything goes...
}
By default, the name of a page is the simple name of the class that declares it. In the above example, the ItemListPage
will fill the navigation panel whenever the browser’s location bar ends with #ItemListPage
. If you prefer a different page name, use the @Page
annotation’s path
attribute:
@Page(path="items")
public class ItemListPage extends Composite {
// Anything goes...
}
Any widget can be a page. This includes Errai UI @Templated
classes! Simply annotate any Errai UI templated class with @Page
, and it will become a page that can be navigated to.
Each application must have exactly one default page . This requirement is enforced at compile time. This default page is displayed when there is no fragment ID present in the browser’s location bar.
Use the role = DefaultPage.class
attribute to declare the default starting page, like this:
@Page(role = DefaultPage.class)
public class WelcomePage extends Composite {
// Anything goes...
}
Pages are looked up as CDI beans, so you can inject other CDI beans into fields or a constructor. Pages can also have @PostConstruct
and @PreDestroy
CDI methods.
There are four annotations related to page lifecycle events: @PageShowing
, @PageShown
, @PageHiding
, and @PageHidden
. These annotations designate methods so a page widget can be notified when it is displayed or hidden:
@Page
public class ItemPage extends VerticalPanel {
@PageShowing
private void preparePage() {
}
@PageHiding
private void unpreparePage() {
}
// Anything goes...
}
Page Lifecycle:
@PageHiding
method on the current (about-to-be-navigated-away-from) page is invoked@PageHidden
method on the just-removed page is invoked@Page
bean in the client-side bean manager (we’ll call this bean "the new page")@PageState
fields in the new page bean (more on this in the next section)@PageShowing
method of the new page is invoked@PageShown
method of the new page is invoked.The @PageShowing
and @PageShown
methods are permitted one optional parameter of type HistoryToken
---more on this in the next section.
The lifespan of a Page instance is governed by CDI scope: Dependent and implict-scoped page beans are instantiated each time the user navigates to them, whereas Singleton and ApplicationScoped beans are created only once over the lifetime of the application. If a particular page is slow to appear because its UI takes a lot of effort to build, try marking it as a singleton.
A page widget will often represent a view on on instance of a class of things. For example, there might be an ItemPage that displays a particular item available at a store. In cases like this, it’s important that the bookmarkable navigation URL includes not only the name of the page but also an identifier for the particular item being displayed.
This is where page state parameters come in. Consider the following page widget:
@Page
public class ItemPage extends VerticalPanel {
@PageState
private int itemId;
// Anything goes...
}
This page would be reachable at a URL like + . Before the page was displayed, the Errai UI Navigation framework would write the [code]+int
value 4
into the itemId
field.
There are three ways to pass state information to a page: by passing a Multimap to TransitionTo.go()
; by passing a Multimap to Navigation.goTo()
, or by including the state information in the fragment identifier of a hyperlink as illustrated in the previous paragraph (use the HistoryToken
class to construct such a fragment ID properly.)
A page widget can have any number of @PageState
fields. The fields can be of any primitive or boxed primitive type (except char
or Character
), String
, or a Collection
, List
, or Set
of the allowable scalar types. Nested collections are not supported.
@PageState
fields can be private, protected, default access, or public. They are always updated by direct field access; never via a setter method. The updates occur just before the @PageShowing
method is invoked.
In addition to receiving page state information via direct writes to @PageState
fields, you can also receive the whole Multimap in the @PageShowing
and @PageShown
methods through a parameter of type HistoryToken
. Whether or not a lifecycle method has such a parameter, the @PageState
fields will still be written as usual.
Page state values are represented in the URL much like HTML form parameters: as key=value pairs separated by the ampersand ( &
) character. Multi-valued page state fields are represented by repeated occurrences of the same key. If a key corresponding to a @PageState
field is absent from the state information passed to the page, the framework writes a default value: null
for scalar Object fields, the JVM default (0 or false) for primitives, and an empty collection for collection-valued fields. To construct and parse state tokens programmatically, use the HistoryToken
class.
The easiest way to declare a link between pages is to inject an instance of TransitionAnchor<P>
, where P
is the class of the target page.
Here is an example declaring an anchor link from the templated welcome page to the item list page. The first code sample would go in WelcomePage.java while the second would go in the WelcomePage.html, the associated html template.
@Page(role = DefaultPage.class)
@Templated
public class WelcomePage extends Composite {
@Inject @DataField TransitionAnchor<ItemListPage> itemLink;
}
<div>
<a data-field="itemLink">Go to Item List Page</a>
</div>
You can inject any number of links into a page. The only restriction is that the target of the link must be a Widget type that is annotated with @Page
. When the user clicks the link Errai will transition to the item list page.
Sometimes it is necessary to manually transition between pages (such as in response to an event being fired). To declare a manual link from one page to another, inject an instance of TransitionTo<P>
, where P
is the class of the target page.
This code declares a manual transition from the welcome page to the item list page:
@Page(role = DefaultPage.class)
public class WelcomePage extends Composite {
@Inject TransitionTo<ItemListPage> startButtonClicked;
}
You do not need to implement the TransitionTo
interface yourself; the framework creates the appropriate instance for you.
As with TransitionAnchor
, the only restriction is that the target of the link must be a Widget type that is annotated with @Page
.
To follow a manual link, simply call the go()
method on an injected TransitionTo
object. For example:
@Page(role = DefaultPage.class)
public class WelcomePage extends Composite {
@Inject TransitionTo<ItemListPage> startButtonClicked;
public void onStartButtonPressed(ClickEvent e) {
startButtonClicked.go();
}
}
Beginning in version 2.4, Errai will automatically attach the Navigation Panel to the Root Panel, but it is possible to override this behaviour by simply adding the Navigation Panel to another component manually. The best time to do this is during application startup, for example in the @PostConstruct
method of your @EntryPoint
class. By using the default behaviour you can allow Errai Navigation to control the full contents of the page, or you can opt to keep some parts of the page (headers, footers, and sidebars, for example) away from Errai Navigation by choosing an alternate location for the Navigation Panel.
The following example reserves space for header and footer content that is not affected by the navigation system:
@EntryPoint
public class Bootstrap {
@Inject
private Navigation navigation;
@PostConstruct
public void clientMain() {
VerticalPanel vp = new VerticalPanel();
vp.add(new HeaderWidget());
vp.add(navigation.getContentPanel());
vp.add(new FooterWidget());
RootPanel.get().add(vp);
}
}
This last example demonstrates a simple approach to defining the page structure with an Errai UI template. The final product is identical to the above example, but in this case the overall page structure is declared in an HTML template rather than being defined programmatically in procedural logic:
@Templated
@EntryPoint
public class OverallPageStrucutre extends Composite {
@Inject
private Navigation navigation;
@Inject @DataField
private HeaderWidget header;
@Inject @DataField
private SimplePanel content;
@Inject @DataField
private FooterWidget footer;
@PostConstruct
public void clientMain() {
// give over the contents of this.content to the navigation panel
content.add(navigation.getContentPanel());
// add this whole templated widget to the root panel
RootPanel.get().add(this);
}
}
By default Errai uses com.google.gwt.user.client.ui.SimplePanel
as a container for navigation panel. Sometimes this is not sufficient and users would prefer using another implementation. For example a com.google.gwt.user.client.ui.SimpleLayoutPanel
that manages child size state.
To provide your own implementation of the navigation panel you must implement org.jboss.errai.ui.nav.client.local.NavigatingContainer
. For example:
public class NavigatingPanel implements NavigatingContainer {
SimplePanel panel = new SimpleLayoutPanel();
public void clear() {
this.panel.clear();
}
public Widget asWidget() {
return panel.asWidget();
}
public Widget getWidget() {
return panel.getWidget();
}
public void setWidget(Widget childWidget) {
panel.add(childWidget);
}
public void setWidget(IsWidget childWidget) {
panel.add(childWidget);
}
}
Then in your GWT module descriptor you need to override the default navigation panel ( org.jboss.errai.ui.nav.client.local.NavigatingContainer
) by adding:
<replace-with class="com.company.application.client.NavigatingPanel">
<when-type-is class="org.jboss.errai.ui.nav.client.local.NavigatingContainer"/>
</replace-with>
Because the pages and links in an Errai Navigation application are declared structurally, the framework gets a complete picture of the app’s navigation structure at compile time. This knowledge is saved out during compilation (and at page reload when in Dev Mode) to the file .errai/navgraph.gv
. You can view the navigation graph using any tool that understands the GraphViz (also known as DOT) file format.
One popular open source tool that can display GraphViz/DOT files is GraphViz . Free downloads are available for all major operating systems.
When rendered, a navigation graph looks like this:
In the rendered graph, the pages are nodes (text surrounded by an ellipse). The starting page is drawn with a heavier stroke. The links are drawn as arrows from one page to another. The labels on these arrows come from the Java field names the TransitionTo objects were injected into.
Starting with version 2.4.0, Errai now supports mobile development. One of the modules that makes this feasible is the Cordova module. It offers a way to integrate with native hardware in an Errai way.
Use the Errai Forge Addon Add Errai Features command and select Errai Cordova to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai Cordova to your project.
When the Cordova module is included you can integrate with native hardware by injecting the native components into your code:
@Templated("#main")
public class KitchenSinkClient extends Composite {
@Inject
Camera camera;
@Inject
@DataField
Button takePicture;
@EventHandler("takePicture")
public void onTakePicktureClicked(ClickEvent event) {
PictureOptions options = new PictureOptions(25);
options.setDestinationType(PictureOptions.DESTINATION_TYPE_DATA_URL);
options.setSourceType(PictureOptions.PICTURE_SOURCE_TYPE_CAMERA);
camera.getPicture(options, new PictureCallback() {
@Override
public void onSuccess(String data) {
image.setUrl(UriUtils.fromSafeConstant("data:image/jpeg;base64," + data));
}
@Override
public void onFailure(String error) {
setGeneralErrorMessage("Could not take picture: " + error);
}
});
}
The components that are supported come from the gwt-phonegap project have a look there form more documentation.
Here are the native hardware components you can inject:
So to integrate with these things all we have to do is @Inject
these classes. There are also a couple of CDI events one can observe to be informed about hardware state:
Example of how to use these events:
private void batteryIsLow(@Observes BatteryLowEvent event) {
//mission accomplished. we can stop the infinite loop now.
}
Errai Security provides a lightweight security API for declaring RPC services and client-side UI elements which require authentication or authorization.
Use the Errai Forge Addon Add Errai Features command and select Errai Security to follow along with this section.
Checkout the Manual Setup Section for instructions on how to manually add Errai Security to your project.
Errai Security provides two main concepts:
Users
Roles
By default the server-side Errai Security module uses PicketLink for authentication. Later on we will explain how to use an alternative backend.
The simplest way to begin experimenting with Errai Security is to add Users and Roles to PicketLink programmatically. Here is some sample server-side code from the Errai Security Demo.
@Singleton
@Startup
public class PicketLinkDefaultUsers {
@Inject
private PartitionManager partitionManager; //
/**
* <p>Loads some users during the first construction.</p>
*/
@PostConstruct
public void create() {
final IdentityManager identityManager = partitionManager.createIdentityManager();
final RelationshipManager relationshipManager = partitionManager.createRelationshipManager();
User john = new User("john");
john.setEmail("john@doe.com");
john.setFirstName("John");
john.setLastName("Doe");
User hacker = new User("hacker");
hacker.setEmail("hacker@illegal.ru");
hacker.setFirstName("Hacker");
hacker.setLastName("anonymous");
identityManager.add(john); //
identityManager.add(hacker);
final Password defaultPassword = new Password("123");
identityManager.updateCredential(john, defaultPassword);
identityManager.updateCredential(hacker, defaultPassword);
Role roleDeveloper = new Role("simple");
Role roleAdmin = new Role("admin");
identityManager.add(roleDeveloper);
identityManager.add(roleAdmin);
relationshipManager.add(new Grant(john, roleDeveloper)); //
relationshipManager.add(new Grant(john, roleAdmin));
}
}
Here are the important things that are happening here:
PicketLink uses the concept of partitions, which are sections that can contain different users and roles. What we really need to make users and roles are the | |
Here we add are new users to the | |
The |
Once you’ve created some users and roles, you’re ready to write some client-side code. Authentication is performed with the org.jboss.errai.security.shared.service.AuthenticationService
via Errai RPC.
Here is some sample code involving the user john from the previous Security Demo excerpt.
Injecting the Caller<AuthenticationService>
:
@Inject Caller<AuthenticationService> authServiceCaller;
Logging in:
authServiceCaller.call(new RemoteCallback<User>() {
@Override
public void callback(User user) {
// handle successful login
}
}, new ErrorCallback<Message>() {
@Override
public boolean error(Message message, Throwable t) {
if (t instanceof AuthenticationException) {
// handle authentication failure
}
// Returning true causes the error to propogate to top-level handlers
return true;
}
}).login("john", "123");
Getting the currently authenticated User:
authServiceCaller.call(new RemoteCallback<User>() {
@Override
public void callback(User user) {
if (!user.equals(User.ANONYMOUS)) {
// Do something because we're logged in.
}
else {
// Do something else because we're not logged in.
}
}
}).getUser();
Logging out:
authServiceCaller.call().logout();
Client-side interceptors are used for caching so that generally only calls to login
and logout
must be sent over the wire. The cache is automatically invalidated when a service throws an UnauthenticatedException
, but it can also be invalidated manually via the SecurityContext
.
The annotation @RestrictedAccess
is the only annotation necessary to secure a resource or UI element. In general, @RestrictedAccess
blocks a resource from users who are not logged in; if an array of roles are passed in, users without the declared roles are prevented access to the annotated resource. Below we will explain how different resources are blocked from unauthorized users.
To secure an Errai RPC service, simply annotate the RPC interface (either the entire type or just a method) with one of the security annotations.
For example:
All methods on this interface require an authenticated user to access:
@Remote
@RestrictedAccess
public interface UserOnlyStuff {
public void someMethod();
public void otherMethod();
}
Here the first method requires an authenticated user, and the second requires a user with the admin role:
@Remote
public interface MixedService {
@RestrictedAccess
public void userService();
@RestrictedAccess(roles = {"admin"})
public void adminService();
}
When access to a secured RPC service is denied an UnauthenticatedException
or UnauthorizedException
is thrown. This error is then transmitted back to the client, where it can be caught with an ErrorCallback
(provided when the RPC is invoked).
Here is how we would invoke the previous MixedService
example with error handling:
MessageBuilder.createCall(new RemoteCallback<Void>() {
@Override
public void callback(Void response) {
// ...
}
}, new ErrorCallback<Message>() { //
@Override
public boolean error(Message message, Throwable t) {
if (t instanceof UnauthenticatedException) {
// User is not logged in.
return false;
}
else if (t instanceof UnauthorizedException) {
// User is logged in but lacked sufficient roles.
return false;
}
else {
// Some other error has happened. Let it propogate.
return true;
}
}
}, MixedService.class).adminService();
This |
Errai Security provides a default global Bus RPC handler that catches any thrown UnauthenticatedException
or UnauthorizedException
and navigates to the page with the LoginPage
or SecurityError
role respectively.
JAX-RS RPCs are secured exactly as bus RPCs. Here is the first example from the previous section, but converted to use JAX-RS instead of the Errai Bus.
@Path("/rest-endpoint")
@RestrictedAccess
public interface UserOnlyStuff {
@Path("/some-method")
@GET
public void someMethod();
@Path("/other-method")
@GET
public void otherMethod();
}
There are two important differences when calling a secured JAX-RS RPC (in contrast to an Errai Bus RPC):
RestErrorCallback
(an interface extending ErrorCallback<Request>
).Because there is no global error-handling, you should always pass a RestErrorCallback
when using a JAX-RS RPC. Errai provides the DefaultRestSecurityErrorCallback
that provides the same default behaviour as the DefaultBusSecurityErrorCallback
mentioned above. It can also optionally wrap a provided callback as demonstrated below:
Injecting a callback Instance
:
@Inject
private Instance<DefaultRestSecurityErrorCallback> defaultCallbackInstance;
Wrapping a custom callback in a default callback:
void callSomeService() {
userOnlyStuffService.call(new RemoteCallback<Void>() {
@Override
public void callback(Void response) {
// Handle success...
}
}, defaultCallbackInstance.get()
.setWrappedErrorCallback(new RestErrorCallback() {
@Override
public boolean error(Request request, Throwable t) {
// Handle error...
// Returning true means the default navigation behaviour will occur
return true;
}
}
)).someMethod();
}
Using the default callback without a wrapped callback:
void callSomeService() {
userOnlyStuffService.call(new RemoteCallback<Void>() {
@Override
public void callback(Void response) {
// Handle success...
}
}, defaultCallbackInstance.get()).someMethod();
}
Any class annotated with @Page
can also be marked with @RestrictedAccess
. By doing so, users will be prevented from navigating to the given page if they are not logged in or lack authorization.
Here are two simple examples:
This page is only for logged in users:
@Page
@RestrictedAccess
public class UserProfilePage extends SimplePanel {
@Inject private Caller<AuthenticationService> authServiceCaller;
private User user;
@PageShowing
private void setupPage() {
authServiceCaller.call(new RemoteCallback<User>() {
@Override
public void callback(User response) {
// We don't have to check if this is a valid user, since the page requires authentication.
user = response;
// do setup...
}
}).getUser();
}
}
This page requires the user and admin roles:
@Page
@RestrictedAccess(roles = {"admin", "user"})
public class AdminManagementPage extends SimplePanel {
}
When a user is denied access to a page they will be redirected to a LoginPage (@Page(role = LoginPage.class))
or SecurityError (@Page(role = SecurityError.class))
page. To direct a user to the page they were trying to reach after successful login, @Inject
the SecurityContext
and invoke the navigateBackOrHome
method.
Security checks performed before page navigation do not use any RPC calls, but are instead performed from a cached (in-memory) instance of the org.jboss.errai.security.shared.api.identity.User
. This prevents the possibility of lengthy delays between page navigation while waiting for RPC return values.
But the drawback is that any attempts to navigate to a secured @Page
before the cache is populated will result in redirection to the LoginPage
— even if the user is in fact logged in.
In practice, this is only likely to happen if a user starts an Errai app with a URL to a secure page while still logged in on the server from a previous session.
One option offered by Errai is to persist the org.jboss.errai.security.shared.api.identity.User
object in a cookie. This can be done by adding the following to ErraiApp.properties
:
errai.security.user_cookie_enabled=true
With this option enabled the User
will be persisted in a browser cookie, which is loaded quickly enough to avoid the described navigation issue. This feature can also be used to allow an application to work offline, or allow the server to log in a user on an initial page request.
The errai.security.user_cookie_enabled=true
setting causes the User
to be stored in plain text. That includes the following information:
If you do not wish to use this feature you will likely want to handle this case in the @PageShowing
method of your LoginPage
. Here is an outline of what you might want to do:
@Page(role = LoginPage.class)
@Templated
public class ExampleLoginPage extends Composite {
@Inject
private SecurityContext securityContext;
@Inject
private Caller<AuthenticationService> authService;
@Inject
@DataField
private Label status;
@PageShowing
public void checkForPendingCache() {
// Check if cache is invalid.
if (!securityContext.isUserCacheValid()) {
// Update the status.
status.setText("loading...");
// Force cache to update by calling getUser
authService.call(new RemoteCallback<User> {
@Override
public void callback(User user) {
/* An interceptor will have updated the cache by now.
So check if we are logged in and redirect if necessary.
*/
if (!user.equals(User