activemq-artemis/examples/jms/replicated-failback-static
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readme.html

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    <title>ActiveMQ JMS Failback using Static selectors Example</title>
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     <h1>JMS Multiple Failover using Replication Example</h1>
     
     <p>This example demonstrates three servers coupled as a live-backup-backup group for high availability (HA) using replication, and a client
     connection failing over from live to backup when the live server is crashed and then to the second backup once the new live fails.</p>

     <p>For more information on ActiveMQ failover and HA, and clustering in general, please see the clustering
     section of the user manual.</p>

     <h2>Example step-by-step</h2>
     <p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
     <p>In this example, the live server is server 1, and the backup server is server 0</p>
     <p>The connection will initially be created to server1, server 1 will crash, and the client will carry on
     seamlessly on server 0, the backup server.</p>

     <ol>
        <li>Get an initial context for looking up JNDI from server #0.</li>
        <pre class="prettyprint">
           initialContext = getContext(0);
        </pre>

        <li>Look up the JMS resources from JNDI on server #0.</li>
        <pre class="prettyprint">
           Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
           ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
        </pre>

        <li>Create a JMS Connection</li>
        <pre class="prettyprint">
           connection = connectionFactory.createConnection();
        </pre>
        
        <li>Create a client acknowledged Session</li>
        <pre class="prettyprint">
           Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
        </pre>
        
        <li>Start the connection to ensure delivery occurs</li>
        <pre class="prettyprint">
           connection.start();
        </pre>

        <li>Create a JMS MessageProducer</li>
        <pre class="prettyprint">
           MessageProducer producer = session.createProducer(queue);
        </pre>

        <li>Create a JMS MessageConsumer</li>
        <pre class="prettyprint">
           MessageConsumer consumer = session.createConsumer(queue);
        </pre>

        <li>Send some messages to server #0, the live server</li>
        <pre class="prettyprint">
           for (int i = 0; i < numMessages; i++)
            {
                TextMessage message = session.createTextMessage("This is text message " + i);
                producer.send(message);
                System.out.println("Sent message: " + message.getText());
            }
        </pre>

        <li>Receive and acknowledge a third of the sent messages</li>
        <pre class="prettyprint">
           TextMessage message0 = null;
            for (int i = 0; i < numMessages / 3; i++)
            {
               message0 = (TextMessage)consumer.receive(5000);
               System.out.println("Got message: " + message0.getText());
            }
            message0.acknowledge();
        </pre>

        <p>When server #0 crashes, the client automatically detects the failure and automatically
            fails over from server #0 to server #1 (in your real program you wouldn't need to sleep).
        </p>
        
        <li>Acknowledging the 2nd third of the sent messages will fail as failover to the backup server has occurred</li>
        <pre class="prettyprint">
           try
             {
               message0.acknowledge();
            }
             catch (JMSException e)
            {
               System.err.println("Got exception while acknowledging message: " + e.getMessage());
            }
        </pre>
        
        <li>Consume again the 2nd third of the messages again. Note that they are not considered as redelivered.</li>
        <pre class="prettyprint">
           for (int i = numMessages / 3; i < (numMessages / 3) * 2; i++)
            {
              message0 = (TextMessage)consumer.receive(5000);
             System.out.printf("Got message: %s (redelivered?: %s)\n", message0.getText(), message0.getJMSRedelivered());
             }
         message0.acknowledge();
        </pre>

         <p>now we Kill server #1 and wait for the server #2 to take over the responsibilities.</p>

        <li>Acknowledging the 3rd third of the sent messages will fail as failover to the backup server has occurred</li>
        <pre class="prettyprint">
           try
            {
               message0.acknowledge();
           }
           catch (JMSException e)
          {
                System.err.println("Got exception while acknowledging message: " + e.getMessage());
             }
        </pre>
        

        <li>Consume again the 3rd third of the messages again. Note that they are not considered as redelivered</li>
        <pre class="prettyprint">
            for (int i = (numMessages / 3) * 2; i < numMessages; i++)
             {
               message0 = (TextMessage)consumer.receive(5000);
               System.out.printf("Got message: %s (redelivered?: %s)\n", message0.getText(), message0.getJMSRedelivered());
            }
             message0.acknowledge();
        </pre>
        
        <li>And finally, <strong>always</strong> remember to close your resources after use, in a <code>finally</code> block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects</li>

        <pre class="prettyprint">
           finally
           {
              if (connection != null)
              {
                 connection.close();
              }

              if (initialContext != null)
              {
                 initialContext.close();
              }
           }
        </pre>

     </ol>
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