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<h1>JMS Interceptor Example</h1>
<p>This example shows you how to implement and configure a simple incoming, server-side interceptor with ActiveMQ.</p>
<p>ActiveMQ allows an application to use an interceptor to hook into the messaging system. All that needs to do is to implement the
Interceptor interface, as defined below: </p>
<pre class="prettyprint">
<code>
public interface Interceptor
{
boolean intercept(Packet packet, RemotingConnection connection) throws ActiveMQException;
}
</code>
</pre>
<p>Once you have your own interceptor class, add it to the activemq-configuration.xml, as follows:</p>
<pre class="prettyprint">
<code>
<configuration>
...
<remoting-incoming-interceptors>
<class-name>org.apache.activemq.jms.example.SimpleInterceptor</class-name>
</remoting-incoming-interceptors>
...
</configuration>
</code>
</pre>
<p>With interceptor, you can handle various events in message processing. In this example, a simple interceptor, SimpleInterceptor, is implemented and configured.
When the example is running, the interceptor will print out each events that are passed in the interceptor. And it will add a string property to the message being
delivered. You can see that after the message is received, there will be a new string property appears in the received message.</p>
<p>With our interceptor we always return <code>true</code> from the <code>intercept</code> method. If we were
to return <code>false</code> that signifies that no more interceptors are to run or the target
is not to be called. Return <code>false</code> to abort processing of the packet.</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>
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<code>InitialContext initialContext = getContext(0);</code>
</pre>
<li>We look-up the JMS queue object from JNDI</li>
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<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>We create a JMS text message that we are going to send.</li>
<pre class="prettyprint">
<code>TextMessage message = session.createTextMessage("This is a text message");</code>
</pre>
<li>We send message to the queue</li>
<pre class="prettyprint">
<code>messageProducer.send(message);</code>
</pre>
<li>We create a JMS Message Consumer to receive the message.</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>The message arrives at the consumer. In this case we use a timeout of 5000 milliseconds but we could use a blocking 'receive()'</li>
<pre class="prettyprint">
<code>TextMessage messageReceived = (TextMessage) messageConsumer.receive(5000);</code>
</pre>
<li>We print out the message and the new property that has been added by the interceptor</li>
<pre class="prettyprint">
<code>System.out.println("Received message [" + messageReceived.getText() + "] with String property: " + messageReceived.getStringProperty("newproperty"));</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>
<pre class="prettyprint">
<code>
finally
{
if (initialContext != null)
{
initialContext.close();
}
if (connection != null)
{
connection.close();
}
}
</code>
</pre>
</ol>
<ol>
<li>The SimpleInterceptor:</li>
<pre class="prettyprint">
<code>
public class SimpleInterceptor implements Interceptor
{
public boolean intercept(Packet packet, RemotingConnection connection) throws ActiveMQException
{
System.out.println("SimpleInterceptor gets called!");
System.out.println("Packet: " + packet.getClass().getName());
System.out.println("RemotingConnection: " + connection.getRemoteAddress());
if (packet instanceof SessionSendMessage)
{
SessionSendMessage realPacket = (SessionSendMessage)packet;
Message msg = realPacket.getServerMessage();
msg.putStringProperty(new SimpleString("newproperty"), new SimpleString("Hello from interceptor!"));
}
return true;
}
}
</code>
</pre>
</ol>
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