Enterprise JavaBeans 3.1, 6th Edition

Message Linking

Message linking is a feature that allows the messages being sent by any enterprise bean to be routed to a specific message-driven bean in the same deployment. By using message linking, you can orchestrate a flow of messages between components in the same application. This is achieved by assigning logical names to destinations instead of using a real JCA endpoint; we may think of message destination references as virtual endpoints (see Figure 8-6).

Figure 8-6. Sending events to the message-link abstraction, which delegates to a real destination

When we discussed this method earlier in the chapter, we never really mentioned where a user registration message was being sent; it could go to an emailing system or some other vendor listening in. However, message linking makes sure that the message goes directly to an explicit message-driven bean that we deploy.

For example, consider the following stateless session bean:

@Stateless(name = "MessageSendingEJB")
@Local(MessageSendingBusiness.class)
public class MessageSendingBean implements MessageSendingBusiness
{
   /**
    * Queue we'll send messages to; logical name as wired from
    * the message-destination-link
    */
   @Resource(name = "jms/MessageDestinationLinkQueue")
   // Name to match message-destination-ref-name
   private Queue queue;

   ...
}

Session Beans Should Not Receive Messages

Session beans respond to calls from EJB clients, and they ...