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<h1>Static Message Selector Example</h1>
<p>This example shows you how to configure a JMS queue with static message selectors (filters).</p>
<p>Static message selectors are ActiveMQ's extension to message selectors as defined in JMS spec 1.1.
Rather than specifying the selector in the application code, static message selectors are defined in one of
ActiveMQ's configuration files, activemq-jms.xml, as an element called 'selector' inside each JMS queue
definition:</p>
<pre class="prettyprint"><code>
<queue name="selectorQueue">
<entry name="/queue/selectorQueue">
<selector string="color='red'"/>
</queue>
</code></pre>
<p>Once configured the queue <code>selectorQueue</code> only delivers messages that are
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.
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>
<p>In the example code, five messages with different <code>color</code> property values are sent to queue <code>selectorQueue</code>.
One consumer is created to receive messages from the queue. Of the five sent messages, two have a <code>color</code> property
set to <code>'red'</code>, one has it set to <code>'blue'</code>, another to <code>'green'</code>,
and one has not the <code>color</code> property at all. The result is that the consumer only gets the two messages
with the <code>'red'</code> color.</p>
<h2>Example step-by-step</h2>
<p><i>To run the example, simply type <code>mvn verify</code> from this directory</i></p>
<ol>
<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>
<pre class="prettyprint">
<code>InitialContext initialContext = getContext();</code>
</pre>
<li>We look-up the JMS queue object from JNDI, this is the queue that has the selector configured with it.</li>
<pre class="prettyprint">
<code>Queue queue = (Queue) initialContext.lookup("/queue/selectorQueue");</code>
</pre>
<li>We look-up the JMS connection factory object from JNDI</li>
<pre class="prettyprint">
<code>ConnectionFactory cf = (ConnectionFactory) initialContext.lookup("/ConnectionFactory");</code>
</pre>
<li>We create a JMS connection</li>
<pre class="prettyprint">
<code>connection = cf.createConnection();</code>
</pre>
<li>We start the connection</li>
<pre class="prettyprint">
<code>connection.start();</code>
</pre>
<li>We create a JMS session. The session is created as non transacted and will auto acknowledge messages.</li>
<pre class="prettyprint">
<code>Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>We create a JMS message producer on the session. This will be used to send the messages.</li>
<pre class="prettyprint">
<code>MessageProducer producer = session.createProducer(queue);</code>
</pre>
<li>We create a JMS message consumer that receives 'red' messages. The message listener will
check the 'color' property on each received message.</li>
<pre class="prettyprint">
<code>
MessageConsumer redConsumer = session.createConsumer(queue);
redConsumer.setMessageListener(new SimpleMessageListener("red"));
</code>
</pre>
<li>We create five messages with different 'color' properties.</li>
<pre class="prettyprint">
<code>
TextMessage redMessage1 = session.createTextMessage("Red-1");
redMessage1.setStringProperty("color", "red");
TextMessage redMessage2 = session.createTextMessage("Red-2");
redMessage2.setStringProperty("color", "red");
TextMessage greenMessage = session.createTextMessage("Green");
greenMessage.setStringProperty("color", "green");
TextMessage blueMessage = session.createTextMessage("Blue");
blueMessage.setStringProperty("color", "blue");
TextMessage normalMessage = session.createTextMessage("No color");
</code>
</pre>
<li>We send those messages.</li>
<pre class="prettyprint">
<code>
producer.send(redMessage1);
System.out.println("Message sent: " + redMessage1.getText());
producer.send(greenMessage);
System.out.println("Message sent: " + greenMessage.getText());
producer.send(blueMessage);
System.out.println("Message sent: " + blueMessage.getText());
producer.send(redMessage2);
System.out.println("Message sent: " + redMessage2.getText());
producer.send(normalMessage);
System.out.println("Message sent: " + normalMessage.getText());
</code>
</pre>
<li>Waiting for the message listener to check the received messages.</li>
<pre class="prettyprint">
<code>
Thread.sleep(5000);
</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>
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