As discussed in the previous sections, interfaces extending core JMS interfaces for Topic help build publish-subscribe components.

Please remember that, to be able to execute the following example programs, you need the message queue environment.

The following is a sample program to publish messages to the Publish-Subscribe topic:

package pubsub;

import java.io.BufferedReader;
import java.io.InputStreamReader;

import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;
import javax.jms.TopicPublisher;
import javax.jms.TopicSession;
import javax.naming.InitialContext;

/**
* Program to publish messages to the topic
* @author Raja
 *
 */
public class PubSubTopicPublisher {

  public static void main(String[] args) {
    PubSubTopicPublisher publisher = new PubSubTopicPublisher();
    publisher.publishMultipleMessages();
  }

  public void publishMultipleMessages() {
    BufferedReader inlineReader = new BufferedReader(
    new InputStreamReader(System.in));
    try {

      //Prompt for the JNDI topic connection factory name
      System.out.println("Enter the Publish Subscribe 
      Topic Connection     Factory name:");
      String connectionFactoryName = inlineReader.readLine();

      // Prompt for topic name for the Pub Sub
      System.out.println("Enter the Publish Subscribe Topic name:");
      String pubsubTopicName = inlineReader.readLine();

      // Look up for the administered objects of Pub Sub
      InitialContext context = new InitialContext();
      TopicConnectionFactory topicConnFactory = 
      (TopicConnectionFactory)     
      context.lookup(connectionFactoryName);
      Topic pubsubTopic = (Topic) context.lookup(pubsubTopicName);
      context.close();

      // Create the JMS objects from administered objects
      TopicConnection topicConnection =     
      topicConnFactory.createTopicConnection();
      TopicSession topicSession =     
      topicConnection.createTopicSession(false,
      Session.AUTO_ACKNOWLEDGE);
      TopicPublisher topicPublisher =     
      topicSession.createPublisher(pubsubTopic);

      // Publish multiple text messages entered one after the other
      String messageContent = null;
      while (true) {
        System.out.println("Enter the new message to send or 'abandon' 
        to exit the program:");
        messageContent = inlineReader.readLine();
        if ("abandon".equals(messageContent))
        break;
        TextMessage textMessage =     
        topicSession.createTextMessage(messageContent);
        topicPublisher.publish(textMessage);
      }

      // Clean Up
      System.out.println("Messages Successfully posted to 
      the queue...");
      inlineReader.close();
      topicConnection.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

While the preceding program helps publish messages to the Publish-Subscribe Topic, the following program is used to subscribe to the Publish-Subscribe Topic, which keeps receiving messages related to the Topic until the quit command is given:

package pubsub;

import java.io.BufferedReader;
import java.io.InputStreamReader;

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

/**
* Program to subscribe for messages from the topic
* 
* @author Raja
*
*/
public class PubSubTopicSubscriber implements MessageListener {
  private boolean quitMessageSubscription = false;
    
  public static void main(String[] args) {
    PubSubTopicSubscriber pubSubTopicSubscriber = 
    new PubSubTopicSubscriber();
    pubSubTopicSubscriber.subscribeTopic();
  }

  public void subscribeTopic() {
    BufferedReader inlineReader = 
    new BufferedReader(new InputStreamReader(System.in));
    try {

      // Prompt for the JNDI topic connection factory name
      System.out.println("Enter the Publish Subscribe 
      Topic Connection Factory name:");
      String connectionFactoryName = inlineReader.readLine();

      // Prompt for topic name for the Pub Sub
      System.out.println("Enter the Publish Subscribe Topic name:");
      String pubsubTopicName = inlineReader.readLine();
      inlineReader.close();

      // Look up for the administered objects of Pub Sub
      InitialContext context = new InitialContext();
      TopicConnectionFactory topicConnFactory = 
      (TopicConnectionFactory)     
      context.lookup(connectionFactoryName);
      Topic pubsubTopic = (Topic) context.lookup(pubsubTopicName);
      context.close();

      // Create the JMS objects from administered objects
      TopicConnection topicConnection =     
      topicConnFactory.createTopicConnection();
      TopicSession topicSession =     
      topicConnection.createTopicSession(
      false, Session.AUTO_ACKNOWLEDGE);
      TopicSubscriber topicSubscriber =     
      topicSession.createSubscriber(pubsubTopic);
      topicSubscriber.setMessageListener(this);
      topicConnection.start();

      // Keep listening to the pub sub until 
      // the Quit subscription     command
      while (!quitMessageSubscription) {
        Thread.sleep(1000);
      }

      // Clean Up
      System.out.println("Messages successfully listened so far,     
      Quitting Subscription!");
      topicConnection.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  
  public void onMessage(Message message) {
    try {
      String messageContent = ((TextMessage) message).getText();
      System.out.println(messageContent);
      if ("quit".equals(messageContent))
      quitMessageSubscription = true;
    } catch (JMSException e) {
      e.printStackTrace();
      quitMessageSubscription = true;
    }
  }
}