188 lines
7.8 KiB
HTML
188 lines
7.8 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis Delayed Redelivery Example</title>
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<link rel="stylesheet" type="text/css" href="../common/common.css" />
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<link rel="stylesheet" type="text/css" href="../common/prettify.css" />
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<script type="text/javascript" src="../common/prettify.js"></script>
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</head>
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<body onload="prettyPrint()">
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<h1>Delayed Redelivery Example</h1>
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<p>This example demonstrates how ActiveMQ Artemis can be configured to provide a delayed redelivery in the case
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where a message needs to be redelivered.</p>
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<p>Delaying redelivery can often be useful in the case that clients regularly fail or roll-back. Without a delayed
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redelivery, the system can get into a "thrashing" state, with delivery being attempted, the client rolling back, and
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delivery being re-attempted ad infinitum in quick succession, using up valuable CPU and network resources.</p>
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<p>Re-delivery occurs when the session is closed with unacknowledged messages. The unacknowledged messages will
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be redelivered.</p>
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<p>By providing a redelivery delay, it can be specified that a delay of, say, 10 seconds is implemented between rollback
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and redelivery. The specific delay is configurable on both a global and per destination level, by using wild-card
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matching on the address settings.</p>
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<h2>Example setup</h2>
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<p>Redelivery delay is specified in the configuration file <a href="src/main/resources/activemq/server0/broker.xml">broker.xml</a>:</p>
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<p>In this example we set the redelivery delay to 5 seconds for the specific example queue. We could set redelivery delay on
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on multiple queues by specifying a wild-card in the match, e.g. <code>match="jms.#"</code> would apply the settings
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to all JMS queues and topics.</p>
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<p>We then consume a message in a transacted session, and rollback, and note that the message is not redelivered until
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after 5 seconds.</p>
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<pre class="prettyprint">
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<code><address-setting match="jms.queue.exampleQueue">
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<redelivery-delay>5000</redelivery-delay>
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</address-setting>
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</code>
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</pre>
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<p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
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<ol>
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<li>Create an initial context to perform the JNDI lookup.</li>
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<pre class="prettyprint">
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<code>initialContext = getContext(0);</code>
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</pre>
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<li>Perform a lookup on the queue</li>
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<pre class="prettyprint">
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<code>Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");</code>
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</pre>
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<li>Perform a lookup on the Connection Factory</li>
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<pre class="prettyprint">
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<code>ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");</code>
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</pre>
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<li>Create a JMS Connection</li>
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<pre class="prettyprint">
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<code>connection = cf.createConnection();</code>
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</pre>
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<li>Create a transacted JMS Session
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<pre class="prettyprint">
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<code>Session session = connection.createSession(true, 0);</code>
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</pre>
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<li>Create a JMS Message Producer</li>
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<pre class="prettyprint">
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<code>MessageProducer producer = session.createProducer(queue);</code>
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</pre>
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<li>Create a Text Message</li>
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<pre class="prettyprint">
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<code>TextMessage message = session.createTextMessage("this is a text message");</code>
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</pre>
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<li>Send the Message</li>
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<pre class="prettyprint">
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<code>producer.send(message);</code>
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</pre>
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<li>We commit the session to effectively send the message to the queue</li>
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<pre class="prettyprint">
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<code>session.commit();</code>
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</pre>
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<li>We create a JMS message consumer on the queue</li>
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<pre class="prettyprint">
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<code>MessageConsumer messageConsumer = session.createConsumer(queue);</code>
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</pre>
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<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>
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<pre class="prettyprint">
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<code>connection.start();</code>
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</pre>
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<li>We receive the message...</li>
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<pre class="prettyprint">
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<code>TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
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System.out.println("1st delivery from " + queue.getQueueName() + ": " + messageReceived.getText());</code>
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</pre>
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<li>...but we roll back the session. the message returns to the queue, but only after a
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5 second delay</li>
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<pre class="prettyprint">
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<code>session.rollback();</code>
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</pre>
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<li>We try to receive the message but it's being delayed</li>
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<pre class="prettyprint">
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<code>
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messageReceived = (TextMessage)messageConsumer.receive(3000);
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if (messageReceived != null)
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{
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return false;
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}
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System.out.println("Redelivery has been delayed so received message is " + messageReceived);
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</code>
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</pre>
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<li>We try and receive the message again, this time we should get it</li>
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<pre class="prettyprint">
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<code>
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messageReceived = (TextMessage)messageConsumer.receive(3000);
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System.out.println("2nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText());
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</code>
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</pre>
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<li>We rollback the session again to cause another redelivery, and we time how long this one takes</code>
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<pre class="prettyprint">
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<code>
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long start = System.currentTimeMillis();
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session.rollback();
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messageReceived = (TextMessage)messageConsumer.receive(8000);
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long end = System.currentTimeMillis();
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System.out.println("3nd delivery from " + queue.getQueueName() + ": " + messageReceived.getText() +
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" after " + (end - start) + " milliseconds.");
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</code>
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</pre>
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<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>
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<pre class="prettyprint">
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<code>finally
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{
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if (initialContext != null)
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{
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initialContext.close();
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}
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if (connection != null)
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{
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connection.close();
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}
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}</code>
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</pre>
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</ol>
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<h2>More information</h2>
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<ul>
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<li>User Manual's <a href="../../../docs/user-manual/en/html_single/index.html#undelivered-messages">Undelivered Messages chapter</a></li>
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</ul>
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</body>
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</html>
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