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<title>HornetQ JMS Scale Down Example</title>
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<h1>JMS Colocated Failover Shared Store Example</h1>
<p>This example demonstrates how you can configure a live server to scale down messages to another live server on shutdown.
<p>This example starts 2 live servers each one with a connector configured for the other live server.</p>
<p>The second live server is killed and its messages are scaled down to the first server on shutdown.</p>
<p>The following shows how to configure the live servers to scale down to one another.</p>
<pre class="prettyprint">
<code><ha-policy template="NONE">
<scale-down>true</scale-down>
<scale-down-connectors>
<connector-ref>server1-connector</connector-ref>
</scale-down-connectors>
</ha-policy>
</code>
</pre>
<p>notice that we have used a template to set some sensible defaults but overridden the backup strategy so back ups
are full servers</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> Get an initial context for looking up JNDI for both servers</li>
<pre class="prettyprint">
<code>
initialContext1 = getContext(1);
initialContext = getContext(0);
</code>
</pre>
<li>Look up the JMS resources from JNDI</li>
<pre class="prettyprint">
<code>
Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
ConnectionFactory connectionFactory1 = (ConnectionFactory)initialContext1.lookup("/ConnectionFactory");
</code>
</pre>
<li>Create a JMS Connections</li>
<pre class="prettyprint">
<code>
connection = connectionFactory.createConnection();
connection1 = connectionFactory1.createConnection();
</code>
</pre>
<li>Create a *non-transacted* JMS Session with client acknowledgement</li>
<pre class="prettyprint">
<code>
Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
Session session1 = connection1.createSession(false, Session.CLIENT_ACKNOWLEDGE);
</code>
</pre>
<li>Create a JMS MessageProducer</li>
<pre class="prettyprint">
<code>
MessageProducer producer = session.createProducer(queue);
MessageProducer producer1 = session1.createProducer(queue);
</code>
</pre>
<li>Send some messages to both servers</li>
<pre class="prettyprint">
<code>
for (int i = 0; i < numMessages; i++)
{
TextMessage message = session.createTextMessage("This is text message " + i);
producer.send(message);
System.out.println("Sent message: " + message.getText());
message = session1.createTextMessage("This is another text message " + i);
producer1.send(message);
System.out.println("Sent message: " + message.getText());
}
</code>
</pre>
<li>Crash server #0, the live server</li>
<pre class="prettyprint">
<code>
killServer(0);
</code>
</pre>
<li>start the connection ready to receive messages</li>
<pre class="prettyprint">
<code>
connection.start();
</code>
</pre>
<li>create a consumer</li>
<pre class="prettyprint">
<code>
MessageConsumer consumer = session.createConsumer(queue);
</code>
</pre>
<li>Receive and acknowledge all of the sent messages, you will notice that messages from both servers are received</li>
<pre class="prettyprint">
<code>
TextMessage message0 = null;
for (int i = 0; i < numMessages; i++)
{
message0 = (TextMessage)consumer.receive(5000);
System.out.println("Got message: " + message0.getText());
}
message0.acknowledge();
</code>
</pre>
<li>And finally (no pun intended), <b>always</b> remember to close your JMS 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 (connection != null)
{
connection.close();
}
if (initialContext != null)
{
initialContext.close();
}
if (connection1 != null)
{
connection1.close();
}
if (initialContext1 != null)
{
initialContext1.close();
}
}
</code>
</pre>
</ol>
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