Java Message Service

Name

JMSDestination — Purpose: Routing

Synopsis

Message objects are always sent to some kind of destination. In the pub/sub model, Message objects are delivered to a topic, identified by a Topic object. In Chapter 2, you learned that the destination of a Message object is established when the TopicPublisher is created:

Topic chatTopic = (Topic)jndi.lookup(topicName);
TopicPublisher publisher = session.createPublisher(chatTopic);
...
TextMessage message = session.createTextMessage(  );
message.setText(username+" : "+text);
publisher.publish(message);

The JMSDestination header identifies the destination of a Message object using a javax.jms.Destination object. The Destination class is the superclass of both Topic (pub/sub) and Queue (p2p). The JMSDestination header is obtained using the Message.getJMSDestination( ) method.

Identifying the destination to which a message was delivered is valuable to JMS clients that consume messages from more than one topic or queue. MessageListener objects might, for example, listen to multiple consumers (TopicSubscriber or QueueReceiver types) so that they receive messages from more than one topic or queue. For example, the Chat client from Chapter 2 could be modified to subscribe to more than one chat topic at a time. In this scenario, the onMessage( ) method of the MessageListener would use the JMSDestination header to identify which chat topic a message came from:

public void onMessage(Message message){ try { TextMessage textMessage = (TextMessage)message; ...