ClientSideLoadBalancingExample.java

/*
 * Copyright 2009 Red Hat, Inc.
 * Red Hat licenses this file to you under the Apache License, version
 * 2.0 (the "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *    http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied.  See the License for the specific language governing
 * permissions and limitations under the License.
 */
package org.hornetq.jms.example;

import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageConsumer;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.naming.InitialContext;

import org.hornetq.common.example.HornetQExample;

/**
 * This example demonstrates how sessions created from a single connection can be load
 * balanced across the different nodes of the cluster.
 * 
 * In this example there are three nodes and we use a round-robin client side load-balancing
 * policy.
 *
 * @author <a href="tim.fox@jboss.com>Tim Fox</a>
 */
public class ClientSideLoadBalancingExample extends HornetQExample
{
   public static void main(final String[] args)
   {
      new ClientSideLoadBalancingExample().run(args);
   }

   @Override
   public boolean runExample() throws Exception
   {
      InitialContext initialContext = null;

      Connection connection = null;

      try
      {
         // Step 1. Get an initial context for looking up JNDI from server 0
         initialContext = getContext(0);

         // Step 2. Look-up the JMS Queue object from JNDI
         Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");

         // Step 3. Look-up a JMS Connection Factory object from JNDI on server 0
         ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");

         // Wait a little while to make sure broadcasts from all nodes have reached the client
         Thread.sleep(5000);

         // Step 4. We create a single connection
         connection = connectionFactory.createConnection();
         
         // Step 5. We create 3 JMS Sessions from the same connection. Since we are using round-robin 
         // load-balancing this should result in each sessions being connected to a different node of the cluster
         Session sessionA = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
         Session sessionB = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
         Session sessionC = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

         // Step 6. We create JMS MessageProducer objects on the sessions
         MessageProducer producerA = sessionA.createProducer(queue);
         MessageProducer producerB = sessionB.createProducer(queue);
         MessageProducer producerC = sessionC.createProducer(queue);

         // Step 7. We send some messages on each producer
         final int numMessages = 10;

         for (int i = 0; i < numMessages; i++)
         {
            TextMessage messageA = sessionA.createTextMessage("A:This is text message " + i);
            producerA.send(messageA);
            System.out.println("Sent message: " + messageA.getText());

            TextMessage messageB = sessionB.createTextMessage("B:This is text message " + i);
            producerB.send(messageB);
            System.out.println("Sent message: " + messageB.getText());

            TextMessage messageC = sessionC.createTextMessage("C:This is text message " + i);
            producerC.send(messageC);
            System.out.println("Sent message: " + messageC.getText());
         }
         
         // Step 8. We start the connection to consume messages
         connection.start();
         
         // Step 9. We consume messages from the 3 session, one at a time.
         // We try to consume one more message than expected from each session. If
         // the session were not properly load-balanced, we would be missing a 
         // message from one of the sessions at the end.
         consume(sessionA, queue, numMessages, "A");
         consume(sessionB, queue, numMessages, "B");
         consume(sessionC, queue, numMessages, "C");

         return true;
      }
      finally
      {
         // Step 10. Be sure to close our resources!

         if (connection != null)
         {
            connection.close();
         }

         if (initialContext != null)
         {
            initialContext.close();
         }
      }
   }
   
   private void consume(Session session, Queue queue, int numMessages, String node) throws JMSException
   {
      MessageConsumer consumer = session.createConsumer(queue);

      for (int i = 0; i < numMessages; i++)
      {
         TextMessage message = (TextMessage)consumer.receive(2000);
         System.out.println("Got message: " + message.getText() + " from node " + node);
      }
      
      System.out.println("receive other message from node " + node + ": " + consumer.receive(2000));

   }
}