activemq-artemis/examples/jms/delayed-redelivery
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readme.html

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    <title>ActiveMQ Delayed Redelivery Example</title>
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     <h1>Delayed Redelivery Example</h1>
     
     <p>This example demonstrates how ActiveMQ can be configured to provide a delayed redelivery in the case
     where a message needs to be redelivered.</p>
     <p>Delaying redelivery can often be useful in the case that clients regularly fail or roll-back. Without a delayed
     redelivery, the system can get into a "thrashing" state, with delivery being attempted, the client rolling back, and
     delivery being re-attempted ad infinitum in quick succession, using up valuable CPU and network resources.</p>
     <p>Re-delivery occurs when the session is closed with unacknowledged messages. The unacknowledged messages will
     be redelivered.</p>
     <p>By providing a redelivery delay, it can be specified that a delay of, say, 10 seconds is implemented between rollback
     and redelivery. The specific delay is configurable on both a global and per destination level, by using wild-card
     matching on the address settings.</p>

     <h2>Example setup</h2>
     <p>Redelivery delay is specified in the configuration file <a href="src/main/resources/hornetq/server0/hornetq-configuration.xml">hornetq-configuration.xml</a>:</p>
     <p>In this example we set the redelivery delay to 5 seconds for the specific example queue. We could set redelivery delay on
     on multiple queues by specifying a wild-card in the match, e.g. <code>match="jms.#"</code> would apply the settings
     to all JMS queues and topics.</p>
     <p>We then consume a message in a transacted session, and rollback, and note that the message is not redelivered until
     after 5 seconds.</p>
     <pre class="prettyprint">
         <code>&lt;address-setting match="jms.queue.exampleQueue"&gt;           
            &lt;redelivery-delay&gt;5000&lt;/redelivery-delay&gt;
         &lt;/address-setting&gt;
         </code>
     </pre>                 
     <p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
     <ol>
        <li>Create an initial context to perform the JNDI lookup.</li>
        <pre class="prettyprint">
           <code>initialContext = getContext(0);</code>
        </pre>

        <li>Perform a lookup on the queue</li>
        <pre class="prettyprint">
           <code>Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");</code>
        </pre>

        <li>Perform a lookup on the Connection Factory</li>
        <pre class="prettyprint">
           <code>ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");</code>
        </pre>

        <li>Create a JMS Connection</li>
        <pre class="prettyprint">
           <code>connection = cf.createConnection();</code>
        </pre>

        <li>Create a transacted JMS Session
        <pre class="prettyprint">
           <code>Session session = connection.createSession(true, 0);</code>
        </pre>

        <li>Create a JMS Message Producer</li>
        <pre class="prettyprint">
          <code>MessageProducer producer = session.createProducer(queue);</code>
       </pre>
       
        <li>Create a Text Message</li>
        <pre class="prettyprint">
            <code>TextMessage message = session.createTextMessage("this is a text message");</code>
        </pre>

        <li>Send the Message</li>
        <pre class="prettyprint">
            <code>producer.send(message);</code>
        </pre>
        
       <li>We commit the session to effectively send the message to the queue</li>
        <pre class="prettyprint">
            <code>session.commit();</code>
        </pre>

        <li>We create a JMS message consumer on the queue</li>
        <pre class="prettyprint">
            <code>MessageConsumer messageConsumer = session.createConsumer(queue);</code>
        </pre>
        
        <li>We start the connection. In order for delivery to occur on any consumers or subscribers on a connection, the connection must be started</li>
        <pre class="prettyprint">
           <code>connection.start();</code>
        </pre>
        
        <li>We receive the message...</li>
        <pre class="prettyprint">
            <code>TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
            System.out.println("1st delivery from " + queue.getQueueName() + ": " + messageReceived.getText());</code>            
        </pre>
        
        <li>...but we roll back the session. the message returns to the queue, but only after a 
            5 second delay</li>
        <pre class="prettyprint">
            <code>session.rollback();</code>
        </pre>
        
        <li>We try to receive the message but it's being delayed</li>
        <pre class="prettyprint">
            <code>
         messageReceived = (TextMessage)messageConsumer.receive(3000);
         
         if (messageReceived != null)
         {
            return false;
         }
         
         System.out.println("Redelivery has been delayed so received message is " + messageReceived);
            
            </code>
        </pre>
  
       <li>We try and receive the message again, this time we should get it</li>
       <pre class="prettyprint">
           <code>             
         messageReceived = (TextMessage)messageConsumer.receive(3000);
         
         System.out.println("2nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText());
           </code>
       </pre>
              
        <li>We rollback the session again to cause another redelivery, and we time how long this one takes</code>
        <pre class="prettyprint">
           <code>
         long start = System.currentTimeMillis();
         
         session.rollback();
                         
         messageReceived = (TextMessage)messageConsumer.receive(8000);
         
         long end = System.currentTimeMillis();
         
         System.out.println("3nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText() +
                            " after " + (end - start) + " milliseconds.");           
           </code>
        </pre>
        
        <li>And finally, <b>always</b> remember to close your JMS connections and 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 (initialContext != null)
              {
                initialContext.close();
              }
              if (connection != null)
              {
                 connection.close();
              }
           }</code>
        </pre>
     </ol>
    
     <h2>More information</h2>
     
     <ul>
        <li>User Manual's <a href="../../../docs/user-manual/en/html_single/index.html#undelivered-messages">Undelivered Messages chapter</a></li>
     </ul>
    
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