166 lines
7.5 KiB
HTML
166 lines
7.5 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis JMS Queue Selector 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 Queue Selector Example</h1>
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<p>This example shows you how to selectively consume messages using message selectors with queue consumers.</p>
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<p>Message selectors are strings with special syntax that can be used in creating consumers. Message consumers
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created with a message selector will only receive messages that match its selector. On message delivery, the JBoss Message
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Server evaluates the corresponding message headers of the messages against each selector, if any, and then delivers
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the 'matched' messages to its consumer. Please consult the JMS 1.1 specification for full details.</p>
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<p>In this example, three message consumers are created on a queue. The first consumer is created with selector
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<code>'color=red'</code>, it only receives messages that
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have a 'color' string property of 'red' value; the second is created with selector <code>'color=green'</code>, it
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only receives messages who have a 'color' string property of
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'green' value; and the third without a selector, which means it receives all messages. To illustrate, three messages
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with different 'color' property values are created and sent.</p>
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<p>Selectors can be used with both queue consumers and topic consumers. The difference is that with queue consumers,
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a message is only delivered to one consumer on the queue, while topic consumers the message will be delivered to every
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matching consumers. In this example, if the third consumer (anyConsumer) were the first consumer created, it will
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consume the first message delivered, therefore there is no chance for the next consumer to get the message, even if it
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matches the selector.</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>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</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>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 messageProducer = session.createProducer(queue);</code>
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</pre>
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<li>We create two selectors.</li>
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<pre class="prettyprint">
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<code>
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String redSelector = "color='red'";
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String greenSelector = "color='green'";
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</code>
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</pre>
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<li>We Create a JMS Message Consumer that receives 'red' messages.</li>
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<pre class="prettyprint">
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<code>
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MessageConsumer redConsumer = session.createConsumer(queue, redSelector);
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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 a second JMS Message Consumer that receives 'green' messages.</li>
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<pre class="prettyprint">
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<code>
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MessageConsumer greenConsumer = session.createConsumer(queue, greenSelector);
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greenConsumer.setMessageListener(new SimpleMessageListener("green"));
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</code>
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</pre>
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<li>We Create another JMS Message Consumer that receives all messages. Please not that the order
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of consumers on a queue is of significance. If the anyConsumer is created before the above two, the
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result will be totally different.</li>
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<pre class="prettyprint">
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<code>
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MessageConsumer anyConsumer = session.createConsumer(queue);
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anyConsumer.setMessageListener(new SimpleMessageListener("any"));
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</code>
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</pre>
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<li>We Create three messages, each has a different color property.</li>
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<pre class="prettyprint">
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<code>
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TextMessage redMessage = session.createTextMessage("Red");
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redMessage.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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</code>
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</pre>
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<li>We send the messages to the topic</li>
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<pre class="prettyprint">
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<code>
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producer.send(redMessage);
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System.out.println("Message sent: " + redMessage.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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</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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