<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->
<html>
<head>
<title>ActiveMQ Artemis Dead Letter Example</title>
<link rel="stylesheet" type="text/css" href="../common/common.css" />
<link rel="stylesheet" type="text/css" href="../common/prettify.css" />
<script type="text/javascript" src="../common/prettify.js"></script>
</head>
<body onload="prettyPrint()">
<h1>Dead Letter Example</h1>
<pre>To run the example, simply type <b>mvn verify</b> from this directory, <br>or <b>mvn -PnoServer verify</b> if you want to start and create the server manually.</pre>
<p>This example shows you how to define and deal with dead letter messages.</p>
<p>Messages can be delivered unsuccessfully (e.g. if the transacted session used to consume them is rolled back).
Such a message goes back to the JMS destination ready to be redelivered.
However, this means it is possible for a message to be delivered again and again without any success and remain in the destination, clogging the system.</p>
<p>To prevent this, messaging systems define dead letter messages: after a specified unsuccessful delivery attempts, the message is removed from the destination
and instead routed to a <em>dead letter address</em> where they can be consumed for further investigation.
<p>
The example will show how to configure ActiveMQ Artemis to route a message to a dead letter address after 3 unsuccessful delivery attempts.<br />
The example will send 1 message to a queue. We will deliver the message 3 times and rollback the session every time.<br />
On the 4th attempt, there won't be any message to consume: it will have been moved to a <em>dead letter address</em>.<br />
We will then consume this dead letter message.
</p>
<h2>Example setup</h2>
<p><em>Dead letter addresses</em> and <em>maximum delivery attempts</em> are defined in the configuration file <a href="src/main/resources/activemq/server0/broker.xml">broker.xml</a>:</p>
<pre class="prettyprint">
<code><address-setting match="jms.queue.exampleQueue">
<dead-letter-address>jms.queue.deadLetterQueue</dead-letter-address>
<max-delivery-attempts>3</max-delivery-attempts>
</address-setting>
</code>
</pre>
<p>This configuration will moved dead letter messages from <code>exampleQueue</code> to the <code>deadLetterQueue</code>.</p>
<p>ActiveMQ Artemis allows to specify either a <code>Queue</code> by prefixing the <code>dead-letter-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 dead letter messages.</p>
<p>The maximum attempts of delivery is <code>3</code>. Once this figure is reached, a message is considered a dead letter message and is moved to
the <code>deadLetterQueue</code>.
<p>Since we want to consume messages from this deadLetterQueue, we also need to add a JNDI binding to perform a lookup.
This is configured in <a href="src/main/resources/activemq/server0/activemq-jms.xml">activemq-jms.xml</a></p>
<pre class="prettyprint">
<code><queue name="deadLetterQueue">
<entry name="/queue/deadLetterQueue"/>
</queue></code>
</pre>
</body>
</html>
dd8203185b