activemq-artemis/examples/jms/scale-down
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readme.html

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  <head>
    <title>ActiveMQ Artemis JMS Scale Down Example</title>
    <link rel="stylesheet" type="text/css" href="../common/common.css" />
    <link rel="stylesheet" type="text/css" href="../common/prettify.css" />
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     <h1>JMS Colocated Failover Shared Store Example</h1>

     <p>This example demonstrates how you can configure a live server to scale down messages to another live server on shutdown.
     <p>This example starts 2 live servers each one with a connector configured for the other live server.</p>
     <p>The second live server is killed and its messages are scaled down to the first server on shutdown.</p>
     <p>The following shows how to configure the live servers to scale down to one another.</p>
     <pre class="prettyprint">
     <code>
     &lt;ha-policy>
         &lt;live-only>
             &lt;scale-down>
                 &lt;connectors>
                     &lt;connector-ref>server0-connector&lt;/connector-ref>
                 &lt;/connectors>
             &lt;/scale-down>
         &lt;/live-only>
     &lt;/ha-policy>
     </code>
     </pre>
     <h2>Example step-by-step</h2>
     <p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>

     <ol>
        <li> Get an initial context for looking up JNDI for both servers</li>
        <pre class="prettyprint">
           <code>
    initialContext1 = getContext(1);
    initialContext = getContext(0);
   </code>
        </pre>

        <li>Look up the JMS resources from JNDI</li>
        <pre class="prettyprint">
           <code>
    Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
    ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
    ConnectionFactory connectionFactory1 = (ConnectionFactory)initialContext1.lookup("/ConnectionFactory");
           </code>
        </pre>

        <li>Create a JMS Connections</li>
        <pre class="prettyprint">
           <code>
    connection = connectionFactory.createConnection();
    connection1 = connectionFactory1.createConnection();
           </code>
        </pre>

        <li>Create a *non-transacted* JMS Session with client acknowledgement</li>
        <pre class="prettyprint">
           <code>
    Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
    Session session1 = connection1.createSession(false, Session.CLIENT_ACKNOWLEDGE);
           </code>
        </pre>

        <li>Create a JMS MessageProducer</li>
        <pre class="prettyprint">
           <code>
    MessageProducer producer = session.createProducer(queue);
    MessageProducer producer1 = session1.createProducer(queue);
           </code>
        </pre>

        <li>Send some messages to both servers</li>
        <pre class="prettyprint">
          <code>
    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());
      message = session1.createTextMessage("This is another text message " + i);
      producer1.send(message);
      System.out.println("Sent message: " + message.getText());
    }
          </code>
        </pre>
        
        <li>Crash server #0, the live server</li>
        <pre class="prettyprint">
          <code>
    killServer(0);
          </code>
        </pre>

        <li>start the connection ready to receive messages</li>
        <pre class="prettyprint">
           <code>
    connection.start();
           </code>
        </pre>
        
        <li>create a consumer</li>
        <pre class="prettyprint">
           <code>
    MessageConsumer consumer = session.createConsumer(queue);
            </code>
        </pre>

        <li>Receive and acknowledge all of the sent messages, you will notice that messages from both servers are received</li>
        <pre class="prettyprint">
           <code>
    TextMessage message0 = null;
    for (int i = 0; i < numMessages; i++)
    {
       message0 = (TextMessage)consumer.receive(5000);
       System.out.println("Got message: " + message0.getText());
    }
    message0.acknowledge();
           </code>
        </pre>

        <li>And finally (no pun intended), <b>always</b> remember to close your JMS 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">
           <code>
    finally
    {
       if (connection != null)
       {
       connection.close();
       }

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

       if (initialContext1 != null)
       {
       initialContext1.close();
       }
    }
           </code>
        </pre>

     </ol>
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