QueueMessageRedistributionExample.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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
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package org.apache.activemq.artemis.jms.example;

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

import org.apache.activemq.artemis.api.jms.ActiveMQJMSClient;
import org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory;

/**
 * This example demonstrates a queue with the same name deployed on two nodes of a cluster.
 * Messages are initially round robin'd between both nodes of the cluster.
 * The consumer on one of the nodes is then closed, and we demonstrate that the "stranded" messages
 * are redistributed to the other node which has a consumer so they can be consumed.
 */
public class QueueMessageRedistributionExample {

   public static void main(final String[] args) throws Exception {
      Connection connection0 = null;

      Connection connection1 = null;

      try {
         // Step 2. Look-up the JMS Queue object from JNDI
         Queue queue = ActiveMQJMSClient.createQueue("exampleQueue");

         // Step 3. Look-up a JMS Connection Factory object from JNDI on server 0
         ConnectionFactory cf0 = new ActiveMQConnectionFactory("tcp://localhost:61616");

         // Step 5. Look-up a JMS Connection Factory object from JNDI on server 1
         ConnectionFactory cf1 = new ActiveMQConnectionFactory("tcp://localhost:61617");

         // Step 6. We create a JMS Connection connection0 which is a connection to server 0
         connection0 = cf0.createConnection();

         // Step 7. We create a JMS Connection connection1 which is a connection to server 1
         connection1 = cf1.createConnection();

         // Step 8. We create a JMS Session on server 0, note the session is CLIENT_ACKNOWLEDGE
         Session session0 = connection0.createSession(false, Session.CLIENT_ACKNOWLEDGE);

         // Step 9. We create a JMS Session on server 1, note the session is CLIENT_ACKNOWLEDGE
         Session session1 = connection1.createSession(false, Session.CLIENT_ACKNOWLEDGE);

         // Step 10. We start the connections to ensure delivery occurs on them
         connection0.start();

         connection1.start();

         // Step 11. We create JMS MessageConsumer objects on server 0 and server 1
         MessageConsumer consumer0 = session0.createConsumer(queue);

         MessageConsumer consumer1 = session1.createConsumer(queue);

         Thread.sleep(1000);

         // Step 12. We create a JMS MessageProducer object on server 0
         MessageProducer producer = session0.createProducer(queue);

         // Step 13. We send some messages to server 0

         final int numMessages = 10;

         for (int i = 0; i < numMessages; i++) {
            TextMessage message = session0.createTextMessage("This is text message " + i);

            producer.send(message);

            System.out.println("Sent message: " + message.getText());
         }

         // Step 14. We now consume those messages on *both* server 0 and server 1.
         // We note the messages have been distributed between servers in a round robin fashion
         // JMS Queues implement point-to-point message where each message is only ever consumed by a
         // maximum of one consumer

         TextMessage message0 = null;

         TextMessage message1 = null;

         for (int i = 0; i < numMessages; i += 2) {
            message0 = (TextMessage) consumer0.receive(5000);

            System.out.println("Got message: " + message0.getText() + " from node 0");

            message1 = (TextMessage) consumer1.receive(5000);

            System.out.println("Got message: " + message1.getText() + " from node 1");
         }

         // Step 15. We acknowledge the messages consumed on node 0. The sessions are CLIENT_ACKNOWLEDGE so
         // messages will not get acknowledged until they are explicitly acknowledged.
         // Note that we *do not* acknowledge the message consumed on node 1 yet.
         message0.acknowledge();

         // Step 16. We now close the session and consumer on node 1. (Closing the session automatically closes the
         // consumer)
         session1.close();

         // Step 17. Since there is no more consumer on node 1, the messages on node 1 are now stranded (no local
         // consumers)
         // so ActiveMQ Artemis will redistribute them to node 0 so they can be consumed.

         for (int i = 0; i < numMessages; i += 2) {
            message0 = (TextMessage) consumer0.receive(5000);

            System.out.println("Got message: " + message0.getText() + " from node 0");
         }

         // Step 18. We ack the messages.
         message0.acknowledge();
      } finally {
         // Step 18. Be sure to close our resources!

         if (connection0 != null) {
            connection0.close();
         }

         if (connection1 != null) {
            connection1.close();
         }
      }
   }
}