152 lines
6.3 KiB
HTML
152 lines
6.3 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ JMS Automatic Reattach 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>JMS Reattach Example</h1>
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<p>This example demonstrates how ActiveMQ connections can be configured to be resilient to
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temporary network failures.</p>
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<p>In the case of a network failure being detected, either as a result of a failure to read/write to the connection,
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or the failure of a pong to arrive back from the server in good time after a ping is sent, instead of
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failing the connection immediately and notifying any user ExceptionListener objects, ActiveMQ
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can be configured to automatically retry the connection, and reattach to the server when it becomes
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available again across the network.</p>
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<p>When the client reattaches to the server it will be able to resume using its sessions and connections
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where it left off</p>
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<p>This is different to client reconnect as the sessions, consumers etc still exist on the server. With reconnect
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The client recreates its sessions and consumers as needed.</p>
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<p>This example starts a single server, connects to it and performs some JMS operations. We then
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simulate failure of the network connection by temporarily stopping the network acceptor on the server.
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(This is done by sending management messages, but that is not central to the purpose of the example).</p>
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<p>We then wait a few seconds, then restart the acceptor. The client reattaches and the session resumes
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as if nothing happened.</p>
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<p>The JMS Connection Factory is configured to reattach automatically by specifying the various reconnect
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related attributes in the <code>activemq-jms.xml</code> file.</p>
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<p>For more details on how to configure this and for clustering in general
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please consult the ActiveMQ user manual.</p>
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<h2>Example step-by-step</h2>
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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>We 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>We create a JMS session. </li>
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<pre class="prettyprint">
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<code>Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
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</pre>
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<li>We create a JMS message producer.</li>
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<pre class="prettyprint">
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<code>MessageProducer messageProducer = session.createProducer(topic);</code>
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</pre>
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<li>We create a JMS text message that we are going to send.</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>We send message to the queue</li>
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<pre class="prettyprint">
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<code>messageProducer.send(message);</code>
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</pre>
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<li>We create a JMS Message Consumer to receive the message.</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>To simulate a temporary problem on the network, we stop the remoting acceptor on the
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server which will cause all client connections to fail.</li>
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<pre class="prettyprint">
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<code>stopAcceptor(initialContext);</code>
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</pre>
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<li>We wait 10 seconds, before restarting the acceptor. During this period the client will be retrying
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to connect. When the acceptor is restarted it will be successful in reconnecting.</li>
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<pre class="prettyprint">
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<code>
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Thread.sleep(10000);
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startAcceptor(initialContext);
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</code>
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</pre>
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<li>We receive the message after reattachment! Note that no exceptions were received by the client.</li>
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<pre class="prettyprint">
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<code>
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TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
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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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</body>
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</html>
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