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<document>  <header>    <product>resin-ee</product>    <title>JMS Listener</title>        <description>          <p>Introduces the JMS message listener configured with JCA.</p>        </description>    <type>tutorial</type>    <tutorial-startpage>send</tutorial-startpage>  </header><body><summary/><s1 title="Files in this tutorial"><deftable><tr><td><viewfile-link file="WEB-INF/web.xml"/>    </td><td>Configures the Queue, MessageSender, MessageListener.</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/MyListener.java"/>    </td><td>The message listener.</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/MessageServlet.java"/>    </td><td>The message servlet</td></tr></deftable></s1><s1 title="Overview"><p>Messaging lets a servlet delegate processing to a batch process eitheron the same machine or on a separate machine.  The servlet creates a messageand sends it to a queue.  The servlet immediately completes and when thebatch process is ready, it processes the message.</p><p>Messaging is therefore comprised of three main components:</p><ul><li>A <var>Producer</var> creates messages and sends them toa <var>Queue</var>.  The Producer could be something like a Servlet.</li><li>A <var>Queue</var> stores the messages from the Produces and providesthem to a Consumer when ready.  The Queue is implemented by themessaging provider.</li><li>A <var>Consumer</var> processes messages as they becomeavailable in the Queue.  The <var>Consumer</var> is typically a beanimplementing the <code>MessageListener</code> interface.</li></ul></s1><s1 title="Producer (MessageServlet)"><p>In this example, the Producer is a Servlet which sends a simple message.The Producer uses a <code>MessageSender</code> configured in the web.xmlto send the message.</p><example title="MessageServlet">String message = "sample message";MessageSender sender = ...; // JNDI lookupsender.send(null, message);</example><p>In this configuration, the <code>MessageSender</code> is a<code>com.caucho.services.message.MessageSender</code>.  It's also possibleto use the full JMS <code>MessageProducer</code> which is more verbose.The <code>MessageSender</code> is an interface available in the opensource <a href="http://www.caucho.com/hessian">Hessian distribution</a>,so it can be used in other application servers as a convenient facade.</p><p>The <code>send</code> method completes as soon asthe message is stored in the queue.  Laster, when a thread is available, theQueue will send the message to the Consumer.</p></s1><s1 title="Consumer (MyListener)"><p>The Queue delivers message to the Consumer one by one.  When theConsumer finishes processing a message the Queue will deliver the nextavailable message.</p><p>The Consumer implements <code>javax.jms.MessageListener</code>, andwill therefore be identical code in any application server.  TheConsumer might even be on a different server or use a differentapplication server.</p><p>In this example, the Consumer just logs the message.</p><example title="MyListener">package example;import java.util.logging.Logger;import java.util.logging.Level;import javax.jms.Message;import javax.jms.TextMessage;import javax.jms.MessageListener;public class MyListener implements MessageListener {  private static final Logger log =    Logger.getLogger(MyListener.class.getName());  public void onMessage(Message message)  {    try {      TextMessage textMessage = (TextMessage) message;      log.info("received: " + textMessage.getText());      _lastMessage = textMessage.getText();    } catch (Throwable e) {      log.log(Level.WARNING, e.toString(), e);    }  }}</example></s1><s1 title="Configuration"><p>The configuration is responsible for three things:</p><ul><li>Configuring the Queue</li><li>Configuring the MessageSender</li><li>Configuring the MessageListener</li></ul><p>The JMS <code>Queue</code> and its <code>ConnectionFactory</code>are configured in the &lt;resource-adapter&gt; section.  Any JMS 1.1implementation may be used for the &lt;connection-factory&gt; and&lt;destination&gt;.</p><p>The &lt;connection-factory&gt; configures the MessageSender and savesit in JNDI.</p><p>The &lt;message-listener&gt; and &lt;endpoint-factory&gt; configuresthe MessageListener.</p><example title="web.xml">&lt;web-app xmlns="http://caucho.com/ns/resin"&gt;  &lt;connector&gt;    &lt;type&gt;com.caucho.jms.jca.ResourceAdapterImpl&lt;/type&gt;    &lt;resource-adapter&gt;      &lt;init&gt;        &lt;connection-factory resin:type="com.caucho.jms.ConnectionFactoryImpl"/&gt;        &lt;destination resin:type="com.caucho.jms.memory.MemoryQueue"/&gt;      &lt;/init&gt;    &lt;/resource-adapter&gt;    &lt;connection-factory jndi-name="jms/sender"                        type="com.caucho.jms.jca.MessageSenderManager"/&gt;    &lt;message-listener type="com.caucho.jms.jca.MessageListenerSpec"&gt;      &lt;endpoint-factory type="com.caucho.jms.jca.ListenerEndpointFactory"&gt;        &lt;init&gt;          &lt;listener resin:type="example.MyListener"/&gt;        &lt;/init&gt;      &lt;/endpoint-factory&gt;    &lt;/message-listener&gt;  &lt;/connector&gt;&lt;/web-app&gt;</example><deftable><tr><th>tag</th><th>meaning</th></tr><tr><td>connector</td><td>top-level configuration for the JCA connector</td></tr><tr><td>type</td><td>The type of the connector.</td></tr><tr><td>resource-adapter</td><td>configures the connector/queue as a whole</td></tr><tr><td>init</td><td>Bean-style initialization for each resource</td></tr><tr><td>connection-factory</td><td>The JMS ConnectionFactory class</td></tr><tr><td>resin:type</td><td>The class name</td></tr><tr><td>destination</td><td>The JMS Queue or Topic</td></tr><tr><td>connection-factory</td><td>Configures a Producer</td></tr><tr><td>jndi-name</td><td>The JNDI name where the resource is stored</td></tr><tr><td>message-listener</td><td>Configures a Consumer</td></tr><tr><td>endpoint-factory</td><td>consumer-specific endpoint type</td></tr><tr><td>listener</td><td>configures the user's listener</td></tr></deftable><deftable><tr><th>class</th><th>meaning</th></tr><tr><td>com.caucho.jms.jca.ResourceAdapterImpl</td><td>Resin's JCA adapterfor the MessageSender and MessageListener</td></tr><tr><td>com.caucho.jms.ConnectionFactoryImpl</td><td>Resin's JMS ConnectionFactory</td></tr><tr><td>com.caucho.jms.memory.MemoryQueue</td><td>Resin's in-memory JMS Queue</td></tr><tr><td>com.caucho.jms.jca.MessageListenerSpec</td><td>Configuration forthe JCA adapter's Consumer</td></tr><tr><td>com.caucho.jms.jca.ListenerEndpointFactory</td><td>Specifies theconfiguration for a MessageListener</td></tr><tr><td>example.MyListener</td><td>Example application code</td></tr></deftable></s1></body></document>
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