The simplest form of the publish/subscribe model: the producer publishes a message, and the consumer reads it using a synchronous receive
/*
* @(#)SynchTopicExample.java 1.3 02/05/02
*
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import javax.jms.*;
/**
* The SynchTopicExample class demonstrates the simplest form of the
* publish/subscribe model: the producer publishes a message, and the
* consumer reads it using a synchronous receive.
* <p>
* The program contains a SimpleProducer class, a SynchConsumer 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.
* <p>
* The program calls methods in the SampleUtilities class.
*
* @author Kim Haase
* @version 1.7, 08/18/00
*/
public class SynchTopicExample {
String topicName = null;
int exitResult = 0;
/**
* The SynchConsumer class fetches a single message from a topic using
* synchronous message delivery.
*
* @author Kim Haase
* @version 1.7, 08/18/00
*/
public class SynchConsumer extends Thread {
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
MessageConsumer msgConsumer = null;
final boolean NOLOCAL = true;
TextMessage inMessage = null;
TextMessage outMessage = null;
MessageProducer msgProducer = null;
/*
* Obtain connection factory.
* Create connection.
* Create session from connection; false means session is not
* transacted.
* Obtain topic name.
*/
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, then start message delivery. Consumer is
* non-local so that it won't receive the message we publish.
* Wait for text message to arrive, then display its contents.
* Close connection and exit.
*/
try {
msgConsumer =
session.createConsumer(topic, null, NOLOCAL);
connection.start();
inMessage = (TextMessage) msgConsumer.receive();
System.out.println("CONSUMER THREAD: Reading message: "
+ inMessage.getText());
/*
* Notify producer that we received a message and it
* can stop broadcasting.
*/
msgProducer = session.createProducer(topic);
outMessage = session.createTextMessage();
outMessage.setText("Done");
msgProducer.send(outMessage);
} 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 SimpleProducer class publishes a single message to a topic.
*
* @author Kim Haase
* @version 1.7, 08/18/00
*/
public class SimpleProducer extends Thread {
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
MessageConsumer producerControlConsumer = null;
final boolean NOLOCAL = true;
MessageProducer msgProducer = null;
TextMessage sentMessage = null;
final String MSG_TEXT = new String("Here is a message ");
Message receivedMessage = null;
/*
* Obtain connection factory.
* Create connection.
* Create session from connection; false means session is not
* transacted.
* Obtain topic name.
*/
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 non-local consumer to receive "Done" message from
* another connection; start delivery.
* Create producer and text message.
* Set message text, display it, and publish message.
* Close connection and exit.
*/
try {
producerControlConsumer =
session.createConsumer(topic, null, NOLOCAL);
connection.start();
/*
* Publish a message once per second until consumer
* reports that it has finished receiving messages.
*/
msgProducer = session.createProducer(topic);
sentMessage = session.createTextMessage();
for (int i = 1; receivedMessage == null; i++) {
sentMessage.setText(MSG_TEXT + i);
System.out.println("PRODUCER THREAD: Publishing message: "
+ sentMessage.getText());
msgProducer.send(sentMessage);
try { Thread.sleep(1000); } catch (InterruptedException ie){}
receivedMessage = producerControlConsumer.receiveNoWait();
}
} 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() {
SynchConsumer synchConsumer = new SynchConsumer();
SimpleProducer simpleProducer = new SimpleProducer();
synchConsumer.start();
simpleProducer.start();
try {
synchConsumer.join();
simpleProducer.join();
} catch (InterruptedException e) {}
}
/**
* Reads the topic name from the command line and displays it. The
* topic must have been created by the jmsadmin tool.
* Calls the run_threads method to execute the program threads.
* Exits program.
*
* @param args the topic used by the example
*/
public static void main(String[] args) {
SynchTopicExample ste = new SynchTopicExample();
if (args.length != 1) {
System.out.println("Usage: java SynchTopicExample <topic_name>");
System.exit(1);
}
ste.topicName = new String(args[0]);
System.out.println("Topic name is " + ste.topicName);
ste.run_threads();
SampleUtilities.exit(ste.exitResult);
}
}
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