140 lines
6.4 KiB
HTML
140 lines
6.4 KiB
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<html>
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<head>
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<title>HornetQ Static Message Selector JMS 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>Static Message Selector Example</h1>
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<p>This example shows you how to configure a JMS queue with static message selectors (filters).</p>
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<p>Static message selectors are HornetQ's extension to message selectors as defined in JMS spec 1.1.
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Rather than specifying the selector in the application code, static message selectors are defined in one of
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HornetQ's configuration files, hornetq-jms.xml, as an element called 'selector' inside each JMS queue
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definition:</p>
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<pre class="prettyprint"><code>
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<queue name="selectorQueue">
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<entry name="/queue/selectorQueue">
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<selector string="color='red'"/>
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</queue>
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</code></pre>
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<p>Once configured the queue <code>selectorQueue</code> only delivers messages that are
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that match the selector; i.e. only the messages whose <code>color</code> property is equal to <code>'red'</code> can be received by its consumers.
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Those that don't match the selector will be dropped by the queue and therefore will never be delivered to any of its consumers.</p>
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<p>In the example code, five messages with different <code>color</code> property values are sent to queue <code>selectorQueue</code>.
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One consumer is created to receive messages from the queue. Of the five sent messages, two have a <code>color</code> property
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set to <code>'red'</code>, one has it set to <code>'blue'</code>, another to <code>'green'</code>,
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and one has not the <code>color</code> property at all. The result is that the consumer only gets the two messages
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with the <code>'red'</code> color.</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</code> from this directory</i></p>
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<ol>
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<li>First we need to get an initial context so we can look-up the JMS connection factory and destination objects from JNDI. This initial context will get it's properties from the <code>client-jndi.properties</code> file in the directory <code>../common/config</code></li>
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<pre class="prettyprint">
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<code>InitialContext initialContext = getContext();</code>
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</pre>
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<li>We look-up the JMS queue object from JNDI, this is the queue that has the selector configured with it.</li>
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<pre class="prettyprint">
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<code>Queue queue = (Queue) initialContext.lookup("/queue/selectorQueue");</code>
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</pre>
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<li>We look-up the JMS connection factory object from JNDI</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 start the connection</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 create a JMS session. The session is created as non transacted and will auto acknowledge messages.</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 on the session. This will be used to send the messages.</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>We create a JMS message consumer that receives 'red' messages. The message listener will
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check the 'color' property on each received message.</li>
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<pre class="prettyprint">
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<code>
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MessageConsumer redConsumer = session.createConsumer(queue);
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redConsumer.setMessageListener(new SimpleMessageListener("red"));
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</code>
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</pre>
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<li>We create five messages with different 'color' properties.</li>
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<pre class="prettyprint">
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<code>
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TextMessage redMessage1 = session.createTextMessage("Red-1");
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redMessage1.setStringProperty("color", "red");
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TextMessage redMessage2 = session.createTextMessage("Red-2");
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redMessage2.setStringProperty("color", "red");
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TextMessage greenMessage = session.createTextMessage("Green");
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greenMessage.setStringProperty("color", "green");
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TextMessage blueMessage = session.createTextMessage("Blue");
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blueMessage.setStringProperty("color", "blue");
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TextMessage normalMessage = session.createTextMessage("No color");
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</code>
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</pre>
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<li>We send those messages.</li>
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<pre class="prettyprint">
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<code>
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producer.send(redMessage1);
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System.out.println("Message sent: " + redMessage1.getText());
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producer.send(greenMessage);
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System.out.println("Message sent: " + greenMessage.getText());
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producer.send(blueMessage);
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System.out.println("Message sent: " + blueMessage.getText());
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producer.send(redMessage2);
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System.out.println("Message sent: " + redMessage2.getText());
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producer.send(normalMessage);
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System.out.println("Message sent: " + normalMessage.getText());
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</code>
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</pre>
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<li>Waiting for the message listener to check the received messages.</li>
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<pre class="prettyprint">
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<code>
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Thread.sleep(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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