2015-01-05 07:45:36 -05:00
|
|
|
<!--
|
|
|
|
|
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.
|
|
|
|
|
-->
|
|
|
|
|
|
2014-10-31 06:20:28 -04:00
|
|
|
<html>
|
|
|
|
|
<head>
|
2014-11-19 03:44:57 -05:00
|
|
|
<title>ActiveMQ JMS Pre-Acknowledge Example</title>
|
2014-10-31 06:20:28 -04:00
|
|
|
<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>JMS Pre-Acknowledge Example</h1>
|
|
|
|
|
|
|
|
|
|
<p>Standard JMS supports three acknowledgement modes: AUTO_ACKNOWLEDGE, CLIENT_ACKNOWLEDGE, and
|
|
|
|
|
DUPS_OK_ACKNOWLEDGE. For a full description on these modes please consult the JMS specification, or any
|
|
|
|
|
JMS tutorial.</p>
|
|
|
|
|
<p>All of these standard modes involve sending acknowledgements from the client to the server. However
|
|
|
|
|
in some cases, you really don't mind losing messages in event of failure, so it would make sense
|
|
|
|
|
to acknowledge the message on the server <b>before</b> delivering it to the client.</p>
|
|
|
|
|
<p>By acknowledging the message before sending to the client, you can avoid extra network traffic and CPU
|
|
|
|
|
work done in sending acknowledgements from client to server.</p>
|
|
|
|
|
<p>The down-side of acknowledging on the server before delivery, is that if the system crashes after acknowledging
|
|
|
|
|
the message, but before the message has been received by the client, then, on recovery, that message
|
|
|
|
|
will be lost. This makes pre-acknowledgement not appropriate for all use cases, but it is very useful for some
|
|
|
|
|
use-cases when you can cope with such loss of messages<p>
|
|
|
|
|
<p>An example of a use-case where it might be a good idea to use pre-acknowledge, is for stock price update
|
|
|
|
|
messages. With these messages it might be ok to lose a message in event of crash, since the next price
|
|
|
|
|
update message will arrive soon, overriding the previous price.</p>
|
2014-11-19 03:44:57 -05:00
|
|
|
<p>In order to use pre-acknowledge functionality with ActiveMQ the session has to be created with
|
|
|
|
|
a special, ActiveMQ specific acknowledgement mode, given by the value of
|
|
|
|
|
<code>ActiveMQJMSConstants.PRE_ACKNOWLEDGE</code>.
|
2014-10-31 06:20:28 -04:00
|
|
|
<h2>Example step-by-step</h2>
|
2015-03-07 11:51:01 -05:00
|
|
|
<p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
|
2014-10-31 06:20:28 -04:00
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>Create an initial context to perform the JNDI lookup.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
initialContext = getContext(0);
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Perform the look-ups</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
|
|
|
|
|
|
|
|
|
|
ConnectionFactory cf = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Create a the JMS objects.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
connection = cf.createConnection();
|
|
|
|
|
|
2014-11-19 03:44:57 -05:00
|
|
|
Session session = connection.createSession(false, ActiveMQSession.PRE_ACKNOWLEDGE);
|
2014-10-31 06:20:28 -04:00
|
|
|
|
|
|
|
|
MessageProducer producer = session.createProducer(queue);
|
|
|
|
|
|
|
|
|
|
MessageConsumer messageConsumer = session.createConsumer(queue);
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Create and send a message.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
TextMessage message1 = session.createTextMessage("This is a text message 1");
|
|
|
|
|
|
|
|
|
|
producer.send(message1);
|
|
|
|
|
|
|
|
|
|
System.out.println("Sent message: " + message1.getText());
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Print out the message count of the queue. The queue contains one message as expected
|
|
|
|
|
delivery has not yet started on the queue.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
int count = getMessageCount(connection);
|
|
|
|
|
|
|
|
|
|
System.out.println("Queue message count is " + count);
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Start the Connection, delivery will now start. Give a little time for delivery to occur.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
connection.start();
|
|
|
|
|
|
|
|
|
|
Thread.sleep(1000);
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Print out the message count of the queue. It should now be zero, since the message has
|
|
|
|
|
already been acknowledged even before the consumer has received it.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
count = getMessageCount(connection);
|
|
|
|
|
|
|
|
|
|
System.out.println("Queue message count is now " + count);
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Finally, receive the message.</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
|
|
|
|
|
|
|
|
|
|
System.out.println("Received message: " + messageReceived.getText());
|
|
|
|
|
</code>
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<li>Be sure to close our resources!</li>
|
|
|
|
|
<pre class="prettyprint">
|
|
|
|
|
<code>
|
|
|
|
|
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#pre-acknowledge">Pre-acknowledgement Mode chapter</a></li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
</body>
|
2015-01-05 07:45:36 -05:00
|
|
|
</html>
|
