Chapter 15. 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.

15.1. 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();

   }

}

15.2. Injecting Java EE resources into a bean

All managed beans may take advantage of Java EE component environment injection using @Resource, @EJB, @PersistenceContext, @PeristenceUnit 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.

15.3. 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 Login 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.

15.4. 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 CDI 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?

15.5. 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 @OrderConnection

   public Connection createOrderConnection() throws JMSException {

    return connectionFactory.createConnection();

   }


   public void closeOrderConnection(@Disposes @OrderConnection Connection connection)

         throws JMSException {

      connection.close();

   }


   @Produces @OrderSession

   public Session createOrderSession(@OrderConnection Connection connection)

         throws JMSException {

      return connection.createSession(true, Session.AUTO_ACKNOWLEDGE);

   }


   public void closeOrderSession(@Disposes @OrderSession Session session)

         throws JMSException {

      session.close();

   }


   @Produces @OrderMessageProducer

   public MessageProducer createOrderMessageProducer(@OrderSession Session session)

         throws JMSException {

      return session.createProducer(orderQueue);

   }


   public void closeOrderMessageProducer(@Disposes @OrderMessageProducer MessageProducer producer)

         throws JMSException {

      producer.close();

   }

}

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

@Inject Order order;

@Inject @OrderMessageProducer MessageProducer producer;

@Inject @OrderSession QueueSession orderSession;


public void sendMessage() {

   MapMessage msg = orderSession.createMapMessage();

   msg.setLong("orderId", order.getId());

   ...

   producer.send(msg);

}