This Post explains Topics in Active MQ  (Message Broker) with Subscribing and Publishing.For this we will write two java clients.As we did for wso2 Message Broker

• TopicSubscriber.java to Subcribe for messages
• TopicPublisher.java to to Publish the messages

Let's Start.

[1] Get Active MQ from http://activemq.apache.org/download.html
[1.1] Start Active MQ from  \bin\activemq.bat
You can see the started server form http://localhost:8161/admin/

[2] Create Porject "Client" on IDE that you preferred
[3] Add activemq-all-5.7.0.jar to lib Dir in the project (activemq-all-5.7.0.jar can be found in root folder)

[4] Creat class "TopicSubscriber.java" to Subcribe for messages

 
package simple;

import java.util.Properties;

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

public class TopicSubscriber {

 private String topicName = "news.sport";
 private String initialContextFactory = ""
 +"org.apache.activemq.jndi.ActiveMQInitialContextFactory";
 private String connectionString = "tcp://"
 +"localhost:61616";
 
 private boolean messageReceived = false;

 public static void main(String[] args) {
  TopicSubscriber subscriber = new TopicSubscriber();
  subscriber.subscribeWithTopicLookup();
 }

 public void subscribeWithTopicLookup() {

  Properties properties = new Properties();
  TopicConnection topicConnection = null;
  properties.put("java.naming.factory.initial", initialContextFactory);
  properties.put("connectionfactory.QueueConnectionFactory",
    connectionString);
  properties.put("topic." + topicName, topicName);
  try {
   InitialContext ctx = new InitialContext(properties);
   TopicConnectionFactory topicConnectionFactory = (TopicConnectionFactory) ctx
     .lookup("QueueConnectionFactory");
   topicConnection = topicConnectionFactory.createTopicConnection();
   System.out
     .println("Create Topic Connection for Topic " + topicName);

   while (!messageReceived) {
    try {
     TopicSession topicSession = topicConnection
       .createTopicSession(false, Session.AUTO_ACKNOWLEDGE);

     Topic topic = (Topic) ctx.lookup(topicName);
     // start the connection
     topicConnection.start();

     // create a topic subscriber
     javax.jms.TopicSubscriber topicSubscriber = topicSession
       .createSubscriber(topic);

     TestMessageListener messageListener = new TestMessageListener();
     topicSubscriber.setMessageListener(messageListener);

     Thread.sleep(5000);
     topicSubscriber.close();
     topicSession.close();
    } catch (JMSException e) {
     e.printStackTrace();
    } catch (NamingException e) {
     e.printStackTrace();
    } catch (InterruptedException e) {
     e.printStackTrace();
    }
   }

  } catch (NamingException e) {
   throw new RuntimeException("Error in initial context lookup", e);
  } catch (JMSException e) {
   throw new RuntimeException("Error in JMS operations", e);
  } finally {
   if (topicConnection != null) {
    try {
     topicConnection.close();
    } catch (JMSException e) {
     throw new RuntimeException(
       "Error in closing topic connection", e);
    }
   }
  }
 }

 public class TestMessageListener implements MessageListener {
  public void onMessage(Message message) {
   try {
    System.out.println("Got the Message : "
      + ((TextMessage) message).getText());
    messageReceived = true;
   } catch (JMSException e) {
    e.printStackTrace();
   }
  }
 }

}

 

[5] Creat class "TopicPublisher.java" to to Publish the messages

 
package simple;

import javax.jms.*;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.util.Properties;

public class TopicPublisher {
 private String topicName = "news.sport";

 private String initialContextFactory = "org.apache.activemq"
+".jndi.ActiveMQInitialContextFactory";
 private String connectionString = "tcp://localhost:61616";
 
 public static void main(String[] args) {
  TopicPublisher publisher = new TopicPublisher();
  publisher.publishWithTopicLookup();
 }

 public void publishWithTopicLookup() {
  Properties properties = new Properties();
  TopicConnection topicConnection = null;
  properties.put("java.naming.factory.initial", initialContextFactory);
  properties.put("connectionfactory.QueueConnectionFactory",
    connectionString);
  properties.put("topic." + topicName, topicName);

  try {
   // initialize
   // the required connection factories
   InitialContext ctx = new InitialContext(properties);
   TopicConnectionFactory topicConnectionFactory = (TopicConnectionFactory) ctx
     .lookup("QueueConnectionFactory");
   topicConnection = topicConnectionFactory.createTopicConnection();

   try {
    TopicSession topicSession = topicConnection.createTopicSession(
      false, Session.AUTO_ACKNOWLEDGE);
    // create or use the topic
    System.out.println("Use the Topic " + topicName);
    Topic topic = (Topic) ctx.lookup(topicName);
    javax.jms.TopicPublisher topicPublisher = topicSession
      .createPublisher(topic);

    String msg = "Hi, I am Test Message";
    TextMessage textMessage = topicSession.createTextMessage(msg);

      topicPublisher.publish(textMessage);
    System.out.println("Publishing message " +textMessage);
    topicPublisher.close();
    topicSession.close();

    Thread.sleep(20);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }

  } catch (JMSException e) {
   throw new RuntimeException("Error in JMS operations", e);
  } catch (NamingException e) {
   throw new RuntimeException("Error in initial context lookup", e);
  }
 }

}

 

[6] Firstly Run "TopicSubscriber.java" and then run "TopicPublisher.java"

Here is out put from both
TopicSubscriber::

Create Topic Connection for Topic news.sport
Got the Message : Hi, I am Test Message


TopicPublisher::

Use the Topic news.sport
Publishing message ActiveMQTextMessage {commandId = 0, responseRequired = false, messageId = ID:Madhuka-THINK-51683-1359787878456-1:1:1:1:1, originalDestination = null, originalTransactionId = null, producerId = null, destination = topic://news.sport, transactionId = null, expiration = 0, timestamp = 1359787878729, arrival = 0, brokerInTime = 0, brokerOutTime = 0, correlationId = null, replyTo = null, persistent = true, type = null, priority = 4, groupID = null, groupSequence = 0, targetConsumerId = null, compressed = false, userID = null, content = null, marshalledProperties = null, dataStructure = null, redeliveryCounter = 0, size = 0, properties = null, readOnlyProperties = false, readOnlyBody = false, droppable = false, text = Hi, I am Test Message}
 [More] Here is full message that we have send to TopicSubscriber. We can get that any parameter in above.
Here is sample to get TimeStamp and ID from JMS message.

 public class TestMessageListener implements MessageListener {
  public void onMessage(Message message) {
   try {
    System.out.println("Got the Message  TimeStamp: "
      +  message.getJMSTimestamp());
    System.out.println("Got the Message JMS ID : "
      +  message.getJMSMessageID());
    messageReceived = true;
   } catch (JMSException e) {
    e.printStackTrace();
   }
  }
 } 

Now go to ActiveMQ server at http://localhost:8161/admin/  See that Topic and message count for that topic. Now you time to check more in 'Active MQ'