O'Reilly - Java Message Service

Java Message Service
JMSReplyTo Purpose: Routing
In some cases, a message producer may want the consumers to reply to a message. The
JMSReplyTo header indicates which address, if any, a JMS consumer should reply to. The
JMSReplyTo header is set explicitly by the JMS client; its contents will be a
javax.jms.Destination object (either Topic or Queue).
In some cases the JMS client will want the message consumers to reply to a temporary
topic or queue set up by the JMS client. Here is an example of a pub/sub JMS client that
creates a temporary topic and uses its Topic object identifier as a JMSReplyTo header:
TopicSession session =
connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);
...
Topic tempTopic = session.createTemporaryTopic( );
...
TextMessage message = session.createTextMessage( );
message.setText(text);
message.setJMSReplyTo(tempTopic);
publisher.publish(message);
When a JMS message consumer receives a message that includes a JMSReplyTo destination,
it can reply using that destination. A JMS consumer is not required to send a reply, but in
some JMS applications clients are programmed to do so. Here is an example of a JMS
consumer that uses the JMSReplyTo header on a received message to send a reply. In this
case, the reply is a simple empty Message object:
Topic chatTopic = ... get topic from somewhere
...
// Publisher is created without a specified Topic
TopicPublisher publisher = session.createPublisher(null);
...
public void onMessage(Message message){
try {
TextMessage textMessage = (TextMessage)message;
Topic replyTopic = (Topic)textMessage.getJMSReplyTo( );
Message replyMessage = session.createMessage( );
publisher.publish(replyTopic, replyMessage);
} catch (JMSException jmse){jmse.printStackTrace( );}
}
The JMSReplyTo destination set by the message producer can be any destination in the
messaging system. Using other established topics or queues allows the message producer
to express routing preferences for the message itself or for replies to that message.
Typically, this kind of routing is used in workflow applications. In a workflow application,
a message represents some task that is processed one step at a time by several JMS clients
- possibly over days. For example, an order message might be processed by sales first, then
inventory, then shipping, and finally accounts receivable. When each JMS client (sales,
inventory, shipping, or accounts receivable) is finished processing the order data, it could
use the JMSReplyTo address to deliver the message to the next step.
164