ch08s07.html

详细介绍了jboss3.0的配置等

Both of these examples are available in the examples directory <tt>org/jboss/docs/jms/client</tt> as <tt>HelloPublisher.java</tt> and <tt>HelloPublisher25.java</tt>.
</p><p>
As we know, it is not only possible to send/publish messages with JMS, but it is also possible to obtain published/sent messages. Time-wise, there are two ways of doing it:</p><div class="itemizedlist"><ul><li><p><a name="d0e4343"></a>Synchronously: This means that you need to manually go and fetch them. We do not show here any examples of how to do that.</p></li><li><p><a name="d0e4346"></a>Asynchronously: This means that you need to register an object that implements the MessageListener interface. It is then up to the JMS provider to invoke this object each time there is a message waiting for you at the destination.</p></li></ul></div><p>
In principle, asynchronous receiving is done the same way for both topics and queues, but the classes and method signatures are different in both cases. First, you must implement a <tt>MessageListener</tt> interface. For simple cases it is often good enough to implement the listener in the same class where you write the other JMS code.
</p><div class="figure"><p><a name="d0e4354"></a><b>Figure 8.28. A <tt>MessageListener</tt></b></p><pre class="programlisting">
public class HelloSubscriber implements MessageListener {

  public void onMessage(Message m) {

    // Unpack the message, be careful when casting to the correct
    // message type. onMessage should not throw any application
    // exceptions.
    try {

      String msg = ((TextMessage)m).getText();
      System.out.println("HelloSubscriber got message: " + msg);

    } catch(JMSException ex) {

      System.err.println("Could not get text message: " + ex);
      ex.printStackTrace();

    }

  }

}

</pre></div><p>
Then you need to create a subscriber/receiver and register the listener with it. You then <span class="emphasis"><i>have</i></span> to start the connection the get the JMS provider to start sending messages to the subscriber/receiver.
</p><p>
For a topic it might look like this:
</p><div class="figure"><p><a name="d0e4368"></a><b>Figure 8.29. Create and start a topic subscriber</b></p><pre class="programlisting">
// Create a subscriber
topicSubscriber = topicSession.createSubscriber(topic);

// Set the message listener, which is this class since we implement
// the MessageListener interface
topicSubscriber.setMessageListener(this);

// OBS! For the message listener to receive any messages the connection
// has to be started.
topicConnection.start();

</pre></div><p>
And for a queue like this:
</p><div class="figure"><p><a name="d0e4375"></a><b>Figure 8.30. Create and start a queue receiver</b></p><pre class="programlisting">
// Create a subscriber
queueReceiver = queueSession.createReceiver(queue);

// Set the message listener, which is this class since we
// implement the MessageListener interface
queueReceiver.setMessageListener(this);

// OBS! For the message listener to receive any messages
// the connection has to be started.
queueConnection.start();

</pre></div><p>
Let's look at a complete example of a topic subscriber:
</p><div class="figure"><p><a name="d0e4382"></a><b>Figure 8.31. Topic subscriber example, from <tt>HelloSubscriber.java</tt> in directory <tt>org/jboss/docs/jms/client</tt></b></p><pre class="programlisting">
package org.jboss.docs.jms.client;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

import javax.jms.TopicConnectionFactory;
import javax.jms.TopicConnection;
import javax.jms.TopicSession;
import javax.jms.TopicSubscriber;
import javax.jms.Topic;
import javax.jms.Message;
import javax.jms.TextMessage;
import javax.jms.Session;
import javax.jms.MessageListener;
import javax.jms.JMSException;

/**
 * &lt;p&gt;Simple JMS client, subscribes for messages on testTopic Topic.
 * &lt;/p&gt;
 *
 * &lt;p&gt;&lt;b&gt;NOTE&lt;/b&gt;This code is a showcase only. It may not provide
 * a stable production example.&lt;/p&gt;
 *
 * @author Peter Antman
 * @version $Revision: 3.1 $
 */
public class HelloSubscriber implements MessageListener {

  /**
   * Topic connection, hold on to this so you may close it.
   */
  TopicConnection topicConnection;

  /**
   * Topic session, hold on to this so you may close it.
   * Also used to create messages.
   */
  TopicSession topicSession;

  /**
   * Subscriber
   */
  TopicSubscriber topicSubscriber;

  /**
   * Destination to subscribe to
   */
  Topic topic;

  /**
   * Sets up all the JMS fixtures.
   *
   * Use close() when finished with object.
   *
   * @param factoryJNDI name of the topic connection factory to look up.
   * @param topicJNDI name of the topic destination to look up
   */
  public HelloSubscriber(String factoryJNDI, String topicJNDI)
    throws JMSException, NamingException
  {

    // Get the initial context
    Context context = new InitialContext();

    // Get the connection factory
    TopicConnectionFactory topicFactory =
      (TopicConnectionFactory)context.lookup(factoryJNDI);

    // Create the connection
    topicConnection = topicFactory.createTopicConnection();

    // Create the session
    topicSession = topicConnection.createTopicSession(
      // No transaction
      false,
      // Auto ack
      Session.AUTO_ACKNOWLEDGE);

    // Look up the destination
    topic = (Topic)context.lookup(topicJNDI);

    // Create a subscriber
    topicSubscriber = topicSession.createSubscriber(topic);

    // Set the message listener, which is this class since we implement
    // the MessageListener interface
    topicSubscriber.setMessageListener(this);

    System.out.println(
      "HelloSubscriber subscribed to topic: " + topicJNDI);

    // OBS! For the message listener to receive any messages the
    // connection has to be started
    topicConnection.start();
  }

  /**
   * Implementation of the MessageListener interface,
   * messages will be received through this method.
   */
  public void onMessage(Message m) {

    // Unpack the message, be careful when casting to the correct
    // message type. onMessage should not throw any application
    // exceptions.
    try {

      String msg = ((TextMessage)m).getText();
      System.out.println("HelloSubscriber got message: " + msg);

    } catch(JMSException ex) {

      System.err.println("Could not get text message: " + ex);
      ex.printStackTrace();

    }

  }

  /**
   * Close session and connection.
   */
  public void close() throws JMSException {

    topicSession.close();
    topicConnection.close();

  }