Mega Code Archive
The use of a message listener in the publishsubscribe model The producer publishes several messages, and the consumer reads them asyn
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/*
* @(#)AsynchTopicExample.java 1.3 02/05/02
*
* Copyright (c) 2000-2002 Sun Microsystems, Inc. All Rights Reserved.
*
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* which is disparaging to Sun.
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* This software is provided "AS IS," without a warranty of any kind. ALL
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* IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
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* INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
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* This software is not designed or intended for use in on-line control of
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*/
import javax.jms.*;
/**
* The AsynchTopicExample class demonstrates the use of a message listener in
* the publish/subscribe model. The producer publishes several messages, and
* the consumer reads them asynchronously.
* <p>
* The program contains a MultipleProducer class, an AsynchConsumer class
* with a listener class, a main method, and a method that runs the consumer
* and producer threads.
* <p>
* Specify a topic name on the command line when you run the program. The
* program also uses a queue named "controlQueue", which should be created
* before you run the program.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
public class AsynchTopicExample {
final String CONTROL_QUEUE = "controlQueue";
String topicName = null;
int exitResult = 0;
/**
* The AsynchConsumer class fetches several messages from a topic
* asynchronously, using a message listener, TextListener.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
public class AsynchConsumer extends Thread {
/**
* The TextListener class implements the MessageListener interface by
* defining an onMessage method for the AsynchConsumer class.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
private class TextListener implements MessageListener {
final SampleUtilities.DoneLatch monitor =
new SampleUtilities.DoneLatch();
/**
* Casts the message to a TextMessage and displays its text.
* A non-text message is interpreted as the end of the message
* stream, and the message listener sets its monitor state to all
* done processing messages.
*
* @param message the incoming message
*/
public void onMessage(Message message) {
if (message instanceof TextMessage) {
TextMessage msg = (TextMessage) message;
try {
System.out.println("CONSUMER THREAD: Reading message: "
+ msg.getText());
} catch (JMSException e) {
System.out.println("Exception in onMessage(): "
+ e.toString());
}
} else {
monitor.allDone();
}
}
}
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
MessageConsumer msgConsumer = null;
TextListener topicListener = null;
try {
connectionFactory =
SampleUtilities.getConnectionFactory();
connection =
connectionFactory.createConnection();
session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
topic = SampleUtilities.getTopic(topicName, session);
} catch (Exception e) {
System.out.println("Connection problem: " + e.toString());
if (connection != null) {
try {
connection.close();
} catch (JMSException ee) {}
}
System.exit(1);
}
/*
* Create consumer.
* Register message listener (TextListener).
* Start message delivery.
* Send synchronize message to producer, then wait till all
* messages have arrived.
* Listener displays the messages obtained.
*/
try {
msgConsumer = session.createConsumer(topic);
topicListener = new TextListener();
msgConsumer.setMessageListener(topicListener);
connection.start();
// Let producer know that consumer is ready.
try {
SampleUtilities.sendSynchronizeMessage("CONSUMER THREAD: ",
CONTROL_QUEUE);
} catch (Exception e) {
System.out.println("Queue probably missing: " + e.toString());
if (connection != null) {
try {
connection.close();
} catch (JMSException ee) {}
}
System.exit(1);
}
/*
* Asynchronously process messages.
* Block until producer issues a control message indicating
* end of publish stream.
*/
topicListener.monitor.waitTillDone();
} catch (JMSException e) {
System.out.println("Exception occurred: " + e.toString());
exitResult = 1;
} finally {
if (connection != null) {
try {
connection.close();
} catch (JMSException e) {
exitResult = 1;
}
}
}
}
}
/**
* The MultipleProducer class publishes several message to a topic.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
public class MultipleProducer extends Thread {
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
MessageProducer msgProducer = null;
TextMessage message = null;
final int NUMMSGS = 20;
final String MSG_TEXT = new String("Here is a message");
try {
connectionFactory =
SampleUtilities.getConnectionFactory();
connection =
connectionFactory.createConnection();
session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
topic = SampleUtilities.getTopic(topicName, session);
} catch (Exception e) {
System.out.println("Connection problem: " + e.toString());
if (connection != null) {
try {
connection.close();
} catch (JMSException ee) {}
}
System.exit(1);
}
/*
* After synchronizing with consumer, create producer.
* Create text message.
* Send messages, varying text slightly.
* Send end-of-messages message.
* Finally, close connection.
*/
try {
/*
* Synchronize with consumer. Wait for message indicating
* that consumer is ready to receive messages.
*/
try {
SampleUtilities.receiveSynchronizeMessages("PRODUCER THREAD: ",
CONTROL_QUEUE, 1);
} catch (Exception e) {
System.out.println("Queue probably missing: " + e.toString());
if (connection != null) {
try {
connection.close();
} catch (JMSException ee) {}
}
System.exit(1);
}
msgProducer = session.createProducer(topic);
message = session.createTextMessage();
for (int i = 0; i < NUMMSGS; i++) {
message.setText(MSG_TEXT + " " + (i + 1));
System.out.println("PRODUCER THREAD: Publishing message: "
+ message.getText());
msgProducer.send(message);
}
// Send a non-text control message indicating end of messages.
msgProducer.send(session.createMessage());
} catch (JMSException e) {
System.out.println("Exception occurred: " + e.toString());
exitResult = 1;
} finally {
if (connection != null) {
try {
connection.close();
} catch (JMSException e) {
exitResult = 1;
}
}
}
}
}
/**
* Instantiates the consumer and producer classes and starts their
* threads.
* Calls the join method to wait for the threads to die.
* <p>
* It is essential to start the consumer before starting the producer.
* In the publish/subscribe model, a consumer can ordinarily receive only
* messages published while it is active.
*/
public void run_threads() {
AsynchConsumer asynchConsumer = new AsynchConsumer();
MultipleProducer multipleProducer = new MultipleProducer();
multipleProducer.start();
asynchConsumer.start();
try {
asynchConsumer.join();
multipleProducer.join();
} catch (InterruptedException e) {}
}
/**
* Reads the topic name from the command line, then calls the
* run_threads method to execute the program threads.
*
* @param args the topic used by the example
*/
public static void main(String[] args) {
AsynchTopicExample ate = new AsynchTopicExample();
if (args.length != 1) {
System.out.println("Usage: java AsynchTopicExample <topic_name>");
System.exit(1);
}
ate.topicName = new String(args[0]);
System.out.println("Topic name is " + ate.topicName);
ate.run_threads();
SampleUtilities.exit(ate.exitResult);
}
}
jms.zip( 65 k)
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