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<title>ActiveMQ JMS Topic Selector Example 1</title>
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<h1>JMS Topic Selector Example 1</h1>
<p>This example shows how messages can be consumed from a topic using Message Selectors.</p>
<p>Consumers (or Subscribers) will only consume messages routed to a topic that match the provided selector</p>
<p>Topics and selectors are a standard part of JMS, please consult the JMS 1.1 specification for full details.</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 = getContext();</code>
</pre>
<li>We look-up the JMS topic object from JNDI</li>
<pre class="prettyprint">
<code>Topic topic = (Topic) initialContext.lookup("/topic/exampleTopic");</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 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 messageProducer = session.createProducer(topic);</code>
</pre>
<li>Create one non-durable subscriber with a specific filter</li>
<pre class="prettyprint">
<code>MessageConsumer messageConsumer1 = session.createConsumer(topic, "someID=1", false);</code>
</pre>
<li>Create a second non-durable subscriber with a specific filter</li>
<pre class="prettyprint">
<code>MessageConsumer messageConsumer2 = session.createConsumer(topic, "someID=2", false);</code>
</pre>
<li>Create a third non-durable subscriber without any filters, and it should receive the complete set of messages</li>
<pre class="prettyprint">
<code>MessageConsumer messageConsumer3 = session.createConsumer(topic, "someID=2", false);</code>
</pre>
<li>Send 20 messages, 10 with someID=1, 10 with someID=2 </li>
<pre class="prettyprint"><code>
for (int i = 1; i < 10; i++)
{
for (int someID = 1; someID <= 2; someID++)
{
TextMessage message1 = session.createTextMessage("This is a text message " + i +
" sent for someID=" +
someID);
message1.setIntProperty("someID", someID);
producer.send(message1);
System.out.println("Sent message: " + message1.getText());
}
}</code></pre>
<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>
<pre class="prettyprint"> <code>connection.start();</code>
</pre>
<li>Consume the messages from MessageConsumer1, filtering out someID=2</li>
<pre class="prettyprint"><code>
for (;;)
{
TextMessage messageReceivedA = (TextMessage)messageConsumer1.receive(1000);
if (messageReceivedA == null)
{
break;
}
System.out.println("messageConsumer1 received " + messageReceivedA.getText() +
" someID = " +
messageReceivedA.getIntProperty("someID"));
}</code></pre>
<li>Consume the messages from MessageConsumer2, filtering out someID=1</li>
<pre class="prettyprint"><code>
for (;;)
{
TextMessage messageReceivedB = (TextMessage)messageConsumer2.receive(1000);
if (messageReceivedB == null)
{
break;
}
System.out.println("messageConsumer2 received " + messageReceivedB.getText() +
" someID = " +
messageReceivedB.getIntProperty("someID"));
}</code></pre>
<li>Consume the messages from MessageConsumer3, receiving the complete set of messages</li>
<pre class="prettyprint"><code>
for (;;)
{
TextMessage messageReceivedC = (TextMessage)messageConsumer3.receive(1000);
if (messageReceivedC == null)
{
break;
}
System.out.println("messageConsumer3 received " + messageReceivedC.getText() +
" someID = " +
messageReceivedC.getIntProperty("someID"));
}</code></pre>
<li>Close the consumers</li>
<pre class="prettyprint"><code>subscriberA.close();</code></pre>
<pre class="prettyprint"><code>subscriberB.close();</code></pre>
<li>Delete the subscriptions when you're done</li>
<pre class="prettyprint"><code>session.unsubscribe("sub-a1");</code></pre>
<pre class="prettyprint"><code>session.unsubscribe("sub-a2");</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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