WildFly 8 and newer come with pre-configured Weld. There is no configuration needed to use Weld (or CDI for that matter). You may still want to fine-tune Weld with additional configuration settings.
Weld is also built into GlassFish from V3 onwards. Since GlassFish V3 is the Java EE reference implementation, it supports all features of CDI. What better way for GlassFish to support these features than to use Weld, the CDI reference implementation? Just package up your CDI application and deploy.
While CDI does not require support for servlet environments, Weld can be used in a servlet container, such as Tomcat or Jetty.
Note
There is a major limitation to using a servlet container; Weld doesn’t
support deploying session beans, injection using @EJB
or @PersistenceContext, or using transactional events in servlet
containers. For enterprise features such as these, you should really be
looking at a Java EE application server.
Weld can be used as a library in an web application that is deployed to
a Servlet container. You should add the weld-servlet-core as a dependency
to your project:
<dependency>
<groupId>org.jboss.weld.servlet</groupId>
<artifactId>weld-servlet-core</artifactId>
<version>2.2.16.Final</version>
</dependency>
All the necessary dependencies (CDI API, Weld core) will be fetched transitively.
Alternatively, there is a shaded version with all the dependencies in a single jar file which is available as:
<dependency>
<groupId>org.jboss.weld.servlet</groupId>
<artifactId>weld-servlet-shaded</artifactId>
<version>2.2.16.Final</version>
</dependency>
In general, weld-servlet uses ServletContainerInitializer mechanism to hook into the life cycle of Servlet 3.x compatible containers.
In special cases when your Servlet container does not support ServletContainerInitializer
or you need more control over the ordering of listeners (e.g. move Weld’s listener)
to the beginning of the list so that CDI context are active during invocation of other listeners)
you can register Weld’s listener manually in the WEB-INF/web.xml file of the application:
<listener>
<listener-class>org.jboss.weld.environment.servlet.Listener</listener-class>
</listener>
Note
There is quite a special use-case where one more special component must
be involved. If you want the session context to be active during
HttpSessionListener.sessionDestroyed() invocation when the session
times out or when all the sessions are destroyed because the deployment
is being removed then org.jboss.weld.servlet.WeldTerminalListener must
be specified as the last one in your web.xml. This listener activates
the session context before other listeners are invoked (note that the
listeners are notified in reverse order when a session is being
destroyed).
Since version 2.2.0.Final only Tomcat 7 and 8 are supported by Weld.
By simply adding weld-servlet you get Tomcat integration automatically.
Weld automatically supports context activation/deactivation and dependency injection into Servlets and Filters. Injection into Servlet listeners works on Tomcat 7.0.50 and newer.
What does not work out of the box is binding BeanManager to JNDI.
Tomcat has a read-only JNDI, so Weld can’t automatically bind the
BeanManager extension SPI. To bind the BeanManager into JNDI, you should
populate META-INF/context.xml in the web root with the following
contents:
<Context>
<Resource name="BeanManager"
auth="Container"
type="javax.enterprise.inject.spi.BeanManager"
factory="org.jboss.weld.resources.ManagerObjectFactory"/>
</Context>
and make it available to your deployment by adding this to the bottom
of web.xml:
<resource-env-ref>
<resource-env-ref-name>BeanManager</resource-env-ref-name>
<resource-env-ref-type>
javax.enterprise.inject.spi.BeanManager
</resource-env-ref-type>
</resource-env-ref>
Tomcat only allows you to bind entries to java:comp/env, so the
BeanManager will be available at java:comp/env/BeanManager
With embedded Tomcat it is necessary to register Weld’s listener programmatically:
public class Main {
public static void main(String[] args) throws ServletException, LifecycleException {
Tomcat tomcat = new Tomcat();
Context ctx = tomcat.addContext("/", new File("src/main/resources").getAbsolutePath());
Tomcat.addServlet(ctx, "hello", HelloWorldServlet.class.getName());
ctx.addServletMapping("/*", "hello");
// ctx.addApplicationListener(Listener.class.getName());
tomcat.start();
tomcat.getServer().await();
}
public static class HelloWorldServlet extends HttpServlet {
@Inject
private BeanManager manager;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/plain");
resp.getWriter().append("Hello from " + manager);
}
}
}
|
Weld’s |
Since version 2.0.2.Final only Jetty 7, 8 and 9 are supported.
Weld supports context activation/deactivation and dependency injection into Servlets and Filters. Injection into Servlet listeners works on Jetty 9.1.1 and newer. This is done automatically for the most part.
Since Jetty 8 the class org.eclipse.jetty.servlet.ServletContextHandler.Decorator
is not visible from the web application. Therefore, one more step is required -
we have to tell Jetty not to hide this system class.
Simply place the following jetty-context.xml file in the WEB-INF dir:
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">
<Configure class="org.eclipse.jetty.webapp.WebAppContext">
<Set name="serverClasses">
<Array type="java.lang.String">
<Item>-org.eclipse.jetty.servlet.ServletContextHandler.Decorator</Item>
</Array>
</Set>
</Configure>
See also Jetty Classloading documentation.
To bind the BeanManager into JNDI, you should either populate
WEB-INF/jetty-env.xml with the following contents:
<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN"
"http://www.eclipse.org/jetty/configure.dtd">
<Configure id="webAppCtx" class="org.eclipse.jetty.webapp.WebAppContext">
<New id="BeanManager" class="org.eclipse.jetty.plus.jndi.Resource">
<Arg> <Ref id="webAppCtx"/> </Arg>
<Arg>BeanManager</Arg>
<Arg>
<New class="javax.naming.Reference">
<Arg>javax.enterprise.inject.spi.BeanManager</Arg>
<Arg>org.jboss.weld.resources.ManagerObjectFactory</Arg>
<Arg/>
</New>
</Arg>
</New>
</Configure>
Or you can configure a special Servlet listener to bind the BeanManager automatically:
<listener>
<listener-class>org.jboss.weld.environment.servlet.BeanManagerResourceBindingListener</listener-class>
</listener>
Just like in Tomcat, you need to make the BeanManager available to your
deployment by adding this to the bottom of web.xml:
<resource-env-ref>
<resource-env-ref-name>BeanManager</resource-env-ref-name>
<resource-env-ref-type>
javax.enterprise.inject.spi.BeanManager
</resource-env-ref-type>
</resource-env-ref>
Jetty only allows you to bind entries to java:comp/env, so the
BeanManager will be available at java:comp/env/BeanManager.
When starting embedded Jetty programmatically from the main method it is necessary to register Weld’s listener:
public class Main {
public static void main(String[] args) throws Exception {
Server jetty = new Server(8080);
WebAppContext context = new WebAppContext();
context.setContextPath("/");
context.setResourceBase("src/main/resources");
jetty.setHandler(context);
context.addServlet(HelloWorldServlet.class, "/*");
context.addEventListener(new Listener());
jetty.start();
jetty.join();
}
public static class HelloWorldServlet extends HttpServlet {
@Inject BeanManager manager;
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/plain");
resp.getWriter().append("Hello from " + manager);
}
}
}
|
Weld’s |
By default, bean archive isolation is enabled. It means that alternatives, interceptors and decorators can be selected/enabled for a bean archive by using a beans.xml descriptor.
This behaviour can be changed by setting the servlet initialization parameter org.jboss.weld.environment.servlet.archive.isolation to false.
In this case, Weld will use a "flat" deployment structure - all bean classes share the same bean archive and all beans.xml descriptors are automatically merged into one. Thus alternatives, interceptors and decorators selected/enabled for a bean archive will be enabled for the whole application.
Note
Bean archive isolation is supported (and enabled by default) from version 2.2.5.Final. Previous versions only operated with the "flat" deployment structure.
CDI 1.1 introduced the bean discovery mode of annotated used for implicit bean archives (see also Section 15.6, “Packaging and deployment”).
This mode may bring additional overhead during container bootstrap. Therefore, Weld Servlet supports the use of Jandex bytecode scanning library to speed up the scanning process. Simply put the jandex.jar on the classpath.
If Jandex is not found on the classpath Weld will use the Java Reflection as a fallback.
In general, an implicit bean archive does not have to contain a beans.xml descriptor. However, such a bean archive is not supported by Weld Servlet, i.e. it’s excluded from discovery.
Note
The bean discovery mode of annotated is supported from version 2.2.5.Final. Previous versions processed implicit bean archives in the same way as explicit bean archives.
In addition to improved integration of the Enterprise Java stack, the "Contexts and Dependency Injection for the Java EE platform" specification also defines a state of the art typesafe, stateful dependency injection framework, which can prove useful in a wide range of application types. To help developers take advantage of this, Weld provides a simple means for being executed in the Java Standard Edition (SE) environment independently of any Java EE APIs.
When executing in the SE environment the following features of Weld are available:
-
Managed beans with
@PostConstructand@PreDestroylifecycle callbacks - Dependency injection with qualifiers and alternatives
-
@Application,@Dependentand@Singletonscopes - Interceptors and decorators
- Stereotypes
- Events
- Portable extension support
EJB beans are not supported.
Weld provides an extension which will boot a CDI bean manager in Java SE, automatically registering all simple beans found on the classpath. The command line parameters can be injected using either of the following:
@Inject @Parameters List<String> params;
@Inject @Parameters String[] paramsArray;
The second form is useful for compatibility with existing classes.
Note
The command line parameters do not become available for injection until
the ContainerInitialized event is fired. If you need access to the
parameters during initialization you can do so via the
public static String[] getParameters() method in StartMain.
Here’s an example of a simple CDI SE application:
import javax.inject.Singleton;
@Singleton
public class HelloWorld
{
public void printHello(@Observes ContainerInitialized event, @Parameters List<String> parameters) {
System.out.println("Hello " + parameters.get(0));
}
}
CDI SE applications can be bootstrapped in the following ways.
Thanks to the power of CDI’s typesafe event model, application
developers need not write any bootstrapping code. The Weld SE module
comes with a built-in main method which will bootstrap CDI for you and
then fire a ContainerInitialized event. The entry point for your
application code would therefore be a simple bean which observes the
ContainerInitialized event, as in the previous example.
In this case your application can be started by calling the provided main method like so:
java org.jboss.weld.environment.se.StartMain <args>
For added flexibility, CDI SE also comes with a bootstrap API which can
be called from within your application in order to initialize CDI and
obtain references to your application’s beans and events. The API
consists of two classes: Weld and WeldContainer.
public class Weld
{
/** Boots Weld and creates and returns a WeldContainer instance, through which
* beans and events can be accesed. */
public WeldContainer initialize() {...}
/** Convenience method for shutting down the container. */
public void shutdown() {...}
}
public class WeldContainer
{
/** Provides access to all beans within the application. */
public Instance<Object> instance() {...}
/** Provides access to all events within the application. */
public Event<Object> event() {...}
/** Provides direct access to the BeanManager. */
public BeanManager getBeanManager() {...}
}
Here’s an example application main method which uses this API to
initialize a bean of type MyApplicationBean.
import org.jboss.weld.environment.se.Weld;
public static void main(String[] args) {
Weld weld = new Weld();
WeldContainer container = weld.initialize();
container.instance().select(MyApplicationBean.class).get();
weld.shutdown();
}
Alternatively the application could be started by firing a custom event
which would then be observed by another simple bean. The following
example fires MyEvent on startup.
org.jboss.weld.environment.se.Weld;
public static void main(String[] args) {
Weld weld = new Weld();
WeldContainer container = weld.initialize();
container.event().select(MyEvent.class).fire( new MyEvent() );
weld.shutdown();
}
In contrast to Java EE applications, Java SE applications place no
restrictions on developers regarding the creation and usage of threads.
Therefore Weld SE provides a custom scope annotation, @ThreadScoped,
and corresponding context implementation which can be used to bind bean
instances to the current thread. It is intended to be used in scenarios
where you might otherwise use ThreadLocal, and does in fact use
ThreadLocal under the hood.
To use the @ThreadScoped annotation you need to enable the
RunnableDecorator which 'listens' for all executions of
Runnable.run() and decorates them by setting up the thread context
beforehand, bound to the current thread, and destroying the context
afterwards.
<beans>
<decorators>
<class>org.jboss.weld.environment.se.threading.RunnableDecorator</class>
</decorator>
</beans>
Note
It is not necessary to use @ThreadScoped in all multithreaded
applications. The thread context is not intended as a replacement for
defining your own application-specific contexts. It is generally only
useful in situations where you would otherwise have used ThreadLocal
directly, which are typically rare.
Weld SE comes packaged as a 'shaded' jar which includes the CDI API,
Weld Core and all dependent classes bundled into a single jar. Therefore
the only Weld jar you need on the classpath, in addition to your
application’s classes and dependent jars, is the Weld SE jar. If you are
working with a pure Java SE application you launch using java, this
may be simpler for you.
If you prefer to work with individual dependencies, then you can use the
weld-core jar which just contains the Weld SE classes. Of course in
this mode you will need to assemble the classpath yourself.
If you work with a dependency management solution such as Maven you can declare a dependency such as:
<dependency>
<groupId>org.jboss.weld.se</groupId>
<artifactId>weld-se</artifactId>
</dependency>
By default, bean archive isolation is enabled. It means that alternatives, interceptors and decorators can be selected/enabled for a bean archive by using a beans.xml descriptor.
This behaviour can be changed by providing a system property org.jboss.weld.se.archive.isolation with value of false. In this case, Weld will use a "flat" deployment structure - all bean classes share the same bean archive and all beans.xml descriptors are automatically merged into one. Thus alternatives, interceptors and decorators selected/enabled for a bean archive will be enabled for the whole application.
Note
Bean archive isolation is supported (and enabled by default) from version 2.2.0.Final. Previous versions only operated with the "flat" deployment structure.
CDI 1.1 introduced the bean discovery mode of annotated used for implicit bean archives (see also Section 15.6, “Packaging and deployment”). This mode may bring additional overhead during container bootstrap.
Therefore, Weld Servlet supports the use of Jandex bytecode scanning library to speed up the scanning process. Simply put the jandex.jar on the classpath.
If Jandex is not found on the classpath Weld will use the Java Reflection as a fallback.
In general, an implicit bean archive does not have to contain a beans.xml descriptor. However, such a bean archive is not supported by Weld SE, i.e. it’s excluded from discovery.
Note
The bean discovery mode of annotated is supported from version 2.2.0.Final. Previous versions processed implicit bean archives in the same way as explicit bean archives.
Weld supports OSGi environment through Pax CDI. For more information on
using Weld in OSGi environment check
Pax CDI
documentation . In addition, Weld comes with a sample application
called Paint which demonstrates how to use CDI with OSGi. Check
examples/osgi/README.md for more information.