Weld 3.1.9.Final - CDI Reference Implementation

Java EE integration

CDI is fully integrated into the Java EE environment. Beans have access to Java EE resources and JPA persistence contexts. They may be used in Unified EL expressions in JSF and JSP pages. They may even be injected into other platform components, such as servlets and message-driven Beans, which are not beans themselves.

Built-in beans

In the Java EE environment, the container provides the following built-in beans, all with the qualifier @Default:

  • the current JTA UserTransaction,

  • a Principal representing the current caller identity,

  • the default Bean Validation ValidationFactory,

  • a Validator for the default ValidationFactory,

  • HttpServletRequest, HttpSession and ServletContext

Note

The FacesContext is not injectable. You can get at it by calling FacesContext.getCurrentInstance(). Alternatively you may define the following producer method:

import javax.enterprise.inject.Produces;

class FacesContextProducer {
   @Produces @RequestScoped FacesContext getFacesContext() {
      return FacesContext.getCurrentInstance();
   }
}

Injecting Java EE resources into a bean

All managed beans may take advantage of Java EE component environment injection using @Resource, @EJB, @PersistenceContext, @PersistenceUnit and @WebServiceRef. We’ve already seen a couple of examples of this, though we didn’t pay much attention at the time:

@Transactional @Interceptor
public class TransactionInterceptor {
   @Resource UserTransaction transaction;

   @AroundInvoke public Object manageTransaction(InvocationContext ctx) throws Exception { ... }
}
@SessionScoped
public class Login implements Serializable {
   @Inject Credentials credentials;
   @PersistenceContext EntityManager userDatabase;
    ...
}

The Java EE @PostConstruct and @PreDestroy callbacks are also supported for all managed beans. The @PostConstruct method is called after all injection has been performed.

Of course, we advise that component environment injection be used to define CDI resources, and that typesafe injection be used in application code.

Calling a bean from a servlet

It’s easy to use a bean from a servlet in Java EE. Simply inject the bean using field or initializer method injection.

public class LoginServlet extends HttpServlet {
   @Inject Credentials credentials;
   @Inject Login login;

   @Override
   public void service(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      credentials.setUsername(request.getParameter("username")):
      credentials.setPassword(request.getParameter("password")):
      login.login();
      if ( login.isLoggedIn() ) {
         response.sendRedirect("/home.jsp");
      }
      else {
         response.sendRedirect("/loginError.jsp");
      }
   }

}

Since instances of servlets are shared across all incoming threads, the bean client proxy takes care of routing method invocations from the servlet to the correct instances of Credentials and Login for the current request and HTTP session.

Calling a bean from a message-driven bean

CDI injection applies to all EJBs, even when they aren’t CDI beans. In particular, you can use CDI injection in message-driven beans, which are by nature not contextual objects.

You can even use interceptor bindings for message-driven Beans.

@Transactional @MessageDriven
public class ProcessOrder implements MessageListener {
   @Inject Inventory inventory;
   @PersistenceContext EntityManager em;

   public void onMessage(Message message) {
      ...
   }
}

Please note that there is no session or conversation context available when a message is delivered to a message-driven bean. Only @RequestScoped and @ApplicationScoped beans are available.

But how about beans which send JMS messages?

JMS endpoints

Sending messages using JMS can be quite complex, because of the number of different objects you need to deal with. For queues we have Queue, QueueConnectionFactory, QueueConnection, QueueSession and QueueSender. For topics we have Topic, TopicConnectionFactory, TopicConnection, TopicSession and TopicPublisher. Each of these objects has its own lifecycle and threading model that we need to worry about.

You can use producer fields and methods to prepare all of these resources for injection into a bean:

import javax.jms.ConnectionFactory;
import javax.jms.Queue;

public class OrderResources {
   @Resource(name="jms/ConnectionFactory")
   private ConnectionFactory connectionFactory;

   @Resource(name="jms/OrderQueue")
   private Queue orderQueue;

   @Produces @Order
   public Connection createOrderConnection() throws JMSException {
    return connectionFactory.createConnection();
   }

   public void closeOrderConnection(@Disposes @Order Connection connection)
         throws JMSException {
      connection.close();
   }

   @Produces @Order
   public Session createOrderSession(@Order Connection connection)
         throws JMSException {
      return connection.createSession(true, Session.AUTO_ACKNOWLEDGE);
   }

   public void closeOrderSession(@Disposes @Order Session session)
         throws JMSException {
      session.close();
   }

   @Produces @Order
   public MessageProducer createOrderMessageProducer(@Order Session session)
         throws JMSException {
      return session.createProducer(orderQueue);
   }

   public void closeOrderMessageProducer(@Disposes @Order MessageProducer producer)
         throws JMSException {
      producer.close();
   }
}

In this example, we can just inject the prepared MessageProducer, Connection or QueueSession:

@Inject Order order;
@Inject @Order MessageProducer producer;
@Inject @Order Session orderSession;

public void sendMessage() {
   MapMessage msg = orderSession.createMapMessage();
   msg.setLong("orderId", order.getId());
   ...
   producer.send(msg);
}

The lifecycle of the injected JMS objects is completely controlled by the container.

Packaging and deployment

CDI doesn’t define any special deployment archive. You can package CDI beans in JARs, EJB JARs or WARs—any deployment location in the application classpath. However, the archive must be a "bean archive".

Unlike CDI 1.0, the CDI 1.1 specification recognizes two types of bean archives. The type determines the way the container discovers CDI beans in the archive.

Note
 CDI 1.1 makes use of a new XSD file for beans.xml descriptor: http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd

Explicit bean archive

An explicit bean archive is an archive which contains a beans.xml file:

  • with a version number of 1.1 (or later), with the bean-discovery-mode of all, or,

  • like in CDI 1.0 – with no version number, or, that is an empty file.

It behaves just like a CDI 1.0 bean archive – i.e. Weld discovers each Java class, interface or enum in such an archive.

Note

The beans.xml file must be located at:

  • META-INF/beans.xml (for jar archives), or,

  • WEB-INF/beans.xml or WEB-INF/classes/META-INF/beans.xml (for WAR archives).

You should never place a beans.xml file in both of the WEB-INF and the WEB-INF/classes/META-INF directories. Otherwise your application would not be portable.
Trimmed bean archive

Optionally beans.xml file in explicit bean archive can include simple trim element. This trimmed bean archive means that ProcessAnnotatedType event is fired for every AnnotatedType, but only types which are annotated with a bean defining annotation or any scope annotation will become beans.

Implicit bean archive

An implicit bean archive is an archive which contains one or more bean classes with a bean defining annotation, or one or more session beans. It can also contain a beans.xml file with a version number of 1.1 (or later), with the bean-discovery-mode of annotated. Weld only discovers Java classes with a bean defining annotation within an implicit bean archive.

Note

The set of bean defining annotations contains:

  • @ApplicationScoped, @SessionScoped, @ConversationScoped and @RequestScoped annotations,

  • all other normal scope types,

  • @Interceptor and @Decorator annotations,

  • all stereotype annotations (i.e. annotations annotated with @Stereotype),

  • and the @Dependent scope annotation.

However, @Singleton is not a bean defining annotation. See 2.5.1. Bean defining annotations to learn more.

Which archive is not a bean archive

Although quite obvious, let’s sum it up:

  • an archive which contains neither a beans.xml file nor any bean class with a bean defining annotation,

  • an archive which contains a beans.xml file with the bean-discovery-mode of none.

Actually, there is one more special rule (designed to retain backward compatibility): an archive which contains a portable extension and no beans.xml is not a bean archive either. However, this is not a very common use case.

Note
 For compatibility with CDI 1.0, each Java EE product (WildFly, GlassFish, etc.) must contain an option to cause an archive to be ignored by the container when no beans.xml is present. Consult specific Java EE product documentation to learn more about such option.

Embeddable EJB container

In an embeddable EJB container, beans may be deployed in any location in which EJBs may be deployed.