The TopicSelectors class demonstrates the use of multiple subscribers and message selectors
/*
* @(#)TopicSelectors.java 1.3 02/05/02
*
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import java.util.*;
import javax.jms.*;
/**
* The TopicSelectors class demonstrates the use of multiple
* subscribers and message selectors.
* <p>
* The program contains a Publisher class, a Subscriber class with a listener
* class, a main method, and a method that runs the subscriber and publisher
* threads.
* <p>
* The Publisher class publishes 30 messages of 6 different types, randomly
* selected, then publishes a "Finished" message. The program creates four
* instances of the Subscriber class, one for each of three types and one that
* listens for the "Finished" message. Each subscriber instance uses a
* different message selector to fetch messages of only one type. The publisher
* displays the messages it sends, and the listener displays the messages that
* the subscribers receive. Because all the objects run in threads, the
* displays are interspersed when the program runs.
* <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 TopicSelectors {
final String CONTROL_QUEUE = "controlQueue";
String topicName = null;
static final String MESSAGE_TYPES[] =
{"Nation/World", "Metro/Region", "Business",
"Sports", "Living/Arts", "Opinion",
// always last type
"Finished"
};
static final String END_OF_MESSAGE_STREAM_TYPE =
MESSAGE_TYPES[MESSAGE_TYPES.length-1];
int exitResult = 0;
/**
* The Publisher class publishes a number of messages. For each, it
* randomly chooses a message type. It creates a message and sets its
* text to a message that indicates the message type.
* It also sets the client property NewsType, which the Subscriber
* objects use as the message selector.
* After a pause to allow the subscribers to get all the messages, the
* publisher sends a final message with a NewsType of "Finished", which
* signals the end of the messages.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
public class Publisher extends Thread {
final int NUM_SUBSCRIBERS;
final int ARRSIZE = 6;
public Publisher(int numSubscribers) {
NUM_SUBSCRIBERS = numSubscribers;
}
/**
* Chooses a message type by using the random number generator
* found in java.util.
*
* @return the String representing the message type
*/
public String chooseType() {
int whichMsg;
Random rgen = new Random();
whichMsg = rgen.nextInt(ARRSIZE);
return MESSAGE_TYPES[whichMsg];
}
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
MessageProducer msgProducer = null;
TextMessage message = null;
int numMsgs = ARRSIZE * 5;
String messageType = 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);
}
/*
* After synchronizing with subscriber, create publisher.
* Create and send news messages.
* Send end-of-messages message.
*/
try {
/*
* Synchronize with subscribers. Wait for messages indicating
* that all subscribers are ready to receive messages.
*/
try {
SampleUtilities.receiveSynchronizeMessages("PUBLISHER THREAD: ",
CONTROL_QUEUE,
NUM_SUBSCRIBERS);
} 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++) {
messageType = chooseType();
message.setStringProperty("NewsType", messageType);
message.setText("Item " + i + ": " + messageType);
System.out.println("PUBLISHER THREAD: Setting message text to: "
+ message.getText());
msgProducer.send(message);
}
message.setStringProperty("NewsType", END_OF_MESSAGE_STREAM_TYPE);
message.setText("That's all the news for today.");
System.out.println("PUBLISHER THREAD: Setting message text to: "
+ message.getText());
msgProducer.send(message);
} catch (JMSException e) {
System.out.println("Exception occurred: " + e.toString());
exitResult = 1;
} finally {
if (connection != null) {
try {
connection.close();
} catch (JMSException e) {
exitResult = 1;
}
}
}
}
}
/**
* Each instance of the Subscriber class creates a subscriber that uses
* a message selector that is based on the string passed to its
* constructor.
* It registers its message listener, then starts listening
* for messages. It does not exit until the message listener sets the
* variable done to true, which happens when the listener gets the last
* message.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
public class Subscriber extends Thread {
String whatKind;
int subscriberNumber;
/**
* The MultipleListener class implements the MessageListener interface
* by defining an onMessage method for the Subscriber class.
*
* @author Kim Haase
* @version 1.6, 08/18/00
*/
private class MultipleListener implements MessageListener {
final SampleUtilities.DoneLatch monitor =
new SampleUtilities.DoneLatch();
/**
* Displays the message text.
* If the value of the NewsType property is "Finished", the message
* listener sets its monitor state to all done processing messages.
*
* @param inMessage the incoming message
*/
public void onMessage(Message inMessage) {
TextMessage msg = (TextMessage) inMessage;
String newsType;
try {
System.out.println("SUBSCRIBER " + subscriberNumber
+ " THREAD: Message received: "
+ msg.getText());
newsType = msg.getStringProperty("NewsType");
if (newsType.equals(TopicSelectors.END_OF_MESSAGE_STREAM_TYPE)) {
System.out.println("SUBSCRIBER " + subscriberNumber
+ " THREAD: Received finished-publishing message");
monitor.allDone();
}
} catch(JMSException e) {
System.out.println("Exception in onMessage(): "
+ e.toString());
}
}
}
/**
* Constructor. Sets whatKind to indicate the type of
* message this Subscriber object will listen for; sets
* subscriberNumber based on Subscriber array index.
*
* @param str a String from the MESSAGE_TYPES array
* @param num the index of the Subscriber array
*/
public Subscriber(String str, int num) {
whatKind = str;
subscriberNumber = num + 1;
}
/**
* Runs the thread.
*/
public void run() {
ConnectionFactory connectionFactory = null;
Connection connection = null;
Session session = null;
Topic topic = null;
String selector = null;
MessageConsumer msgConsumer = null;
MultipleListener multipleListener = new MultipleListener();
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 subscriber with message selector.
* Start message delivery.
* Send synchronize message to publisher, then wait till all
* messages have arrived.
* Listener displays the messages obtained.
*/
try {
selector = new String("NewsType = '" + whatKind + "'" +
" OR NewsType = '" + END_OF_MESSAGE_STREAM_TYPE + "'");
System.out.println("SUBSCRIBER " + subscriberNumber
+ " THREAD: selector is \"" + selector + "\"");
msgConsumer =
session.createConsumer(topic, selector, false);
msgConsumer.setMessageListener(multipleListener);
connection.start();
// Let publisher know that subscriber is ready.
try {
SampleUtilities.sendSynchronizeMessage("SUBSCRIBER "
+ subscriberNumber
+ " 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 appropriate news messages.
* Block until publisher issues a finished message.
*/
multipleListener.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;
}
}
}
}
}
/**
* Creates an array of Subscriber objects, one for each of three message
* types including the Finished type, and starts their threads.
* Creates a Publisher object and starts its thread.
* Calls the join method to wait for the threads to die.
*/
public void run_threads() {
final int NUM_SUBSCRIBERS = 3;
Subscriber subscriberArray[] = new Subscriber[NUM_SUBSCRIBERS];
Publisher publisher = new Publisher(NUM_SUBSCRIBERS);
subscriberArray[0] = new Subscriber(MESSAGE_TYPES[2], 0);
subscriberArray[0].start();
subscriberArray[1] = new Subscriber(MESSAGE_TYPES[3], 1);
subscriberArray[1].start();
subscriberArray[2] = new Subscriber(MESSAGE_TYPES[4], 2);
subscriberArray[2].start();
publisher.start();
for (int i = 0; i < subscriberArray.length; i++) {
try {
subscriberArray[i].join();
} catch (InterruptedException e) {}
}
try {
publisher.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) {
TopicSelectors ts = new TopicSelectors();
if (args.length != 1) {
System.out.println("Usage: java TopicSelectors <topic_name>");
System.exit(1);
}
ts.topicName = new String(args[0]);
System.out.println("Topic name is " + ts.topicName);
ts.run_threads();
SampleUtilities.exit(ts.exitResult);
}
}
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