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<h1>JMS Expiration Example</h1>
<p>This example shows you how to configure ActiveMQ so messages are expipired after a certain time..</p>
<p>Messages can be retained in the messaging system for a limited period of time before being removed.
JMS specification states that clients should not receive messages that have been expired (but it does not guarantee this will not happen).</p>
<p>ActiveMQ can assign a <em>expiry address</em> to a given queue so that when messages are expired, they are removed from the queue and
routed to an this address. These "expired" messages can later be consumed for further inspection.
<p>
The example will send 1 message with a short <em>time-to-live</em> to a queue. We will wait for the message to expire and checks that the message
is no longer in the queue it was sent to.
We will instead consume it from an <em>expiry queue</em> where it was moved when it expired.
</p>
<h2>Example setup</h2>
<p>Expiry destinations are defined in the configuration file <a href="server0/activemq-configuration.xml">activemq-configuration.xml</a>:</p>
<pre class="prettyprint">
<code><address-setting match="jms.queue.exampleQueue">
<expiry-address>jms.queue.expiryQueue</expiry-address>
</address-setting>
</code>
</pre>
<p>This configuration will moved expired messages from the <code>exampleQueue</code> to the <code>expiryQueue</code></p>
<p>ActiveMQ allows to specify either a <code>Queue</code> by prefixing the <code>expiry-address</code> with <code>jms.queue.</code>
or a <code>Topic</code> by prefixing with <code>jms.topic.</code>.<br />
In this example, we will use a <code>Queue</code> to hold the expired messages.</p>
<p>Since we want to consume messages from this expiryQueue, we also need to add a JNDI binding to perform a lookup.
This is configured in <a href="server0/activemq-jms.xml">activemq-jms.xml</a></p>
<pre class="prettyprint">
<code><queue name="expiryQueue">
<entry name="/queue/expiryQueue"/>
</queue></code>
</pre>
</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</li>
<pre class="prettyprint">
<code>Queue queue = (Queue) initialContext.lookup("/queue/exampleQueue");</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>Messages sent by this producer will be retained for 1s (1000ms) before expiration</li>
<pre class="prettyprint">
<code>producer.setTimeToLive(1000);</code>
</pre>
<li>We create a text messages</li>
<pre class="prettyprint">
<code>TextMessage message = session.createTextMessage("this is a text message");</code>
</pre>
<li>We send the message to the queue</li>
<pre class="prettyprint">
<code>producer.send(message);</code>
</pre>
<li>We sleep a little bit to let the message expire</li>
<pre class="prettyprint">
<code>Thread.sleep(5000);</code>
</pre>
<p>We will now try to consume the message from the queue but it won't be there since it has expired</p>
<li>We create a JMS message consumer on the queue</li>
<pre class="prettyprint">
<code>MessageConsumer messageConsumer = session.createConsumer(queue);</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>We try to receive a message from the queue. Since there is none, the call will timeout after 5000ms and <code>messageReceived</code> will be <code>null</code>
<pre class="prettyprint">
<code>TextMessage messageReceived = (TextMessage) messageConsumer.receive(5000);
System.out.println("Received message from " + queue.getQueueName() + ": " + messageReceived);</code>
</pre>
<p>However, we have configured ActiveMQ to send any expired messages to the <code>expiryQueue</code>.
We will now consume messages from this expiry queue and receives the <em>expired</em> message.</p>
<li>We look up the JMS <em>expiry queue</em> object from JNDI</li>
<pre class="prettyprint">
<code>Queue expiryQueue = (Queue)initialContext.lookup("/queue/expiryQueue");</code>
</pre>
<li>We create a JMS message consumer on the expiry queue</li>
<pre class="prettyprint">
<code>MessageConsumer expiryConsumer = session.createConsumer(expiryQueue);</code>
</pre>
<li>We consume a message from the expiry queue:</li>
<pre class="prettyprint">
<code>messageReceived = (TextMessage)expiryConsumer.receive(5000);</code>
</pre>
<li>The message consumed from the <em>expiry queue</em> has the <em>same content</em> than the message which was sent to the <em>queue</em>
<pre class="prettyprint">
<code>System.out.println("Received message from " + expiryQueue.getQueueName() + ": " + messageReceived.getText());</code>
</pre>
<p>JMS does not specify the notion of expiry queue. From JMS point of view, the message received from the expiry queue
is a <strong>different</strong> message than the message expired from the queue: the two messages have the same content (properties and body) but
their JMS headers differ.<br />
ActiveMQ defines additional properties to correlate the message received from the expiry queue with the
message expired from the queue</p>
<li>The expired message's destination is the expiry queue</li>
<pre class="prettyprint">
<code>System.out.println("Destination of the expired message: " + ((Queue)messageReceived.getJMSDestination()).getQueueName());</code>
</pre>
<li>The expired message has its own <em>expiration time</em> (its time to live in the <strong>expiry queue</strong>)</li>
<pre class="prettyprint">
<code>System.out.println("Expiration time of the expired message (relative to the expiry queue): " + messageReceived.getJMSExpiration());</code>
</pre>
<p>As we have not defined a time-to-live for the expiry queue, messages sent to the expiry queue will be kept forever (their JMS Expiration value is 0)</p>
<li>The <strong>origin destination</strong> is stored in the <code>_HORNETQ_ORIG_DESTINATION</code> property
<pre class="prettyprint">
<code>System.out.println("*Origin destination* of the expired message: " + messageReceived.getStringProperty("_HORNETQ_ORIG_DESTINATION"));</code>
</pre>
<li>The <strong>actual expiration time</strong> (when the message was expired from the queue) is stored in the <code>_HORNETQ_ACTUAL_EXPIRY</code> property
<pre class="prettyprint">
<code>System.out.println("*Actual expiration time* of the expired message: " + messageReceived.getLongProperty("_HORNETQ_ACTUAL_EXPIRY"));</code>
</pre>
</p>
<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>
<h2>More information</h2>
<ul>
<li>User Manual's <a href="../../../docs/user-manual/en/html_single/index.html#message-expiry">Message Expiry chapter</a></li>
</ul>
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