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<h1>JMS XA Heuristic Example</h1>
<p>This example shows you how to make an XA heuristic decision through the ActiveMQ Management Interface.</p>
<p>A heuristic decision is a unilateral decision to commit or rollback an XA transaction branch after it has
been prepared. </p>
<p>In this example we simulate a transaction manager to control the transactions. First we create an XASession
and enlist it in a transaction through its XAResource. We then send a text message, 'hello' and end/prepare the transaction
on the XAResource, but neither commit nor roll back the transaction. Another transaction is created and
associated with the same XAResource, and a second message, 'world' is sent on behalf of the second transaction. Again we leave
the second transaction in prepare state.
Then we get the MBeanServerConnection object to manipulate the prepared transactions. To illustrate, we roll back the first
transaction but commit the second. This will result in that only the message 'world' is received. </p>
<p>This example uses JMX to manipulate transactions in a ActiveMQ Server. For details on JMX facilities with ActiveMQ,
please look at the JMX Example.</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(0);</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 perform a lookup on the XA Connection Factory</li>
<pre class="prettyprint">
<code>XAConnectionFactory cf = (XAConnectionFactory) initialContext.lookup("/XAConnectionFactory");</code>
</pre>
<li>We create a JMS XAConnection</li>
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<code>connection = cf.createXAConnection();</code>
</pre>
<li>We Start the connection</li>
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<code>connection.start();</code>
</pre>
<li>We create a JMS XASession</li>
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<code>XASession xaSession = connection.createXASession();</code>
</pre>
<li>We create a normal session</li>
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<code>Session normalSession = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);</code>
</pre>
<li>We create a normal Message Consumer</li>
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<code>
MessageConsumer normalConsumer = normalSession.createConsumer(queue);
normalConsumer.setMessageListener(new SimpleMessageListener());
</code>
</pre>
<li>We get the JMS Session</li>
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<code>Session session = xaSession.getSession();</code>
</pre>
<li>We create a message producer</li>
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<code>MessageProducer producer = session.createProducer(queue); </code>
</pre>
<li>We create two Text Messages</li>
<pre class="prettyprint">
<code>
TextMessage helloMessage = session.createTextMessage("hello");
TextMessage worldMessage = session.createTextMessage("world");
</code>
</pre>
<li>We create a transaction</li>
<pre class="prettyprint">
<code>Xid xid1 = new XidImpl("xa-example1".getBytes(), 1, UUIDGenerator.getInstance().generateStringUUID().getBytes());</code>
</pre>
<li>We get the JMS XAResource</li>
<pre class="prettyprint">
<code>XAResource xaRes = xaSession.getXAResource();</code>
</pre>
<li>We begin the Transaction work</li>
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<code>xaRes.start(xid1, XAResource.TMNOFLAGS);</code>
</pre>
<li>We do work, sending hello message.</li>
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<code>
normalProducer.send(helloMessage);
</code>
</pre>
<li>We stop the work for xid1</li>
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<code>xaRes.end(xid1, XAResource.TMSUCCESS);</code>
</pre>
<li>We prepare xid1</li>
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<code>xaRes.prepare(xid1);</code>
</pre>
<li>We check the none should be received.</li>
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<code>checkNoMessageReceived();</code>
</pre>
<li>We create another transaction </li>
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<code>Xid xid2 = new XidImpl("xa-example2".getBytes(), 1, UUIDGenerator.getInstance().generateStringUUID().getBytes());</code>
</pre>
<li>We begin the transaction work</li>
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<code>xaRes.start(xid2, XAResource.TMNOFLAGS);</code>
</pre>
<li>We send the second message</li>
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<code>producer.send(worldMessage);</code>
</pre>
<li>We stop the work for xid2</li>
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<code>xaRes.end(xid2, XAResource.TMSUCCESS);</code>
</pre>
<li>We prepare xid2</li>
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<code>xaRes.prepare(xid2);</code>
</pre>
<li>Again, no messages should be received!</li>
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<code>checkNoMessageReceived();</code>
</pre>
<li>We create JMX Connector to connect to the server's MBeanServer.</li>
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<code>
JMXConnector connector = JMXConnectorFactory.connect(new JMXServiceURL(JMX_URL), new HashMap<String, String>());
</code>
</pre>
<li>We retrieve the MBeanServerConnection</li>
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<code>MBeanServerConnection mbsc = connector.getMBeanServerConnection();</code>
</pre>
<li>We list the prepared transactions</li>
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<code>
ObjectName serverObject = ObjectNameBuilder.DEFAULT.getMessagingServerObjectName();
String[] infos = (String[])mbsc.invoke(serverObject, "listPreparedTransactions", null, null);
System.out.println("Prepared transactions: ");
for (String i : infos)
{
System.out.println(i);
}
</code>
</pre>
<li>We roll back the first transaction</li>
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<code>mbsc.invoke(serverObject, "rollbackPreparedTransaction", new String[] {XidImpl.toBase64String(xid1)}, new String[]{"java.lang.String"});</code>
</pre>
<li>We commit the second one</li>
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<code>mbsc.invoke(serverObject, "commitPreparedTransaction", new String[] {XidImpl.toBase64String(xid2)}, new String[]{"java.lang.String"});</code>
</pre>
<li>We check the result, only the 'world' message received</li>
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<code>checkMessageReceived("world");</code>
</pre>
<li>We check the prepared transaction again, should have none.</li>
<pre class="prettyprint">
<code>
infos = (String[])mbsc.invoke(serverObject, "listPreparedTransactions", null, null);
System.out.println("No. of prepared transactions now: " + infos.length);
</code>
</pre>
<li>We close the JMX connector.</li>
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<code>connector.close();</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>
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<code>finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}</code>
</pre>
</ol>
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