Programming

package chap2.chat;
 
import javax.jms.*;
import javax.naming.*;
import java.io.*;
import java.io.InputStreamReader;
import java.util.Properties;
 
public class Chat implements javax.jms.MessageListener{
    private TopicSession pubSession;
    private TopicSession subSession;
    private TopicPublisher publisher;
    private TopicConnection connection;
    private String username;
 
    /* Constructor. Establish JMS publisher and subscriber */
    public Chat(String topicName, String username, String password)
    throws Exception {
        // Obtain a JNDI connection
        Properties env = new Properties( );
        // ... specify the JNDI properties specific to the vendor
 
        InitialContext jndi = new InitialContext(env);
 
        // Look up a JMS connection factory
        TopicConnectionFactory conFactory =
        (TopicConnectionFactory)jndi.lookup("TopicConnectionFactory");
 
        // Create a JMS connection
        TopicConnection connection =
        conFactory.createTopicConnection(username,password);
 
        // Create two JMS session objects
        TopicSession pubSession =
        connection.createTopicSession(false,
                                      Session.AUTO_ACKNOWLEDGE);
        TopicSession subSession =
        connection.createTopicSession(false,
                                      Session.AUTO_ACKNOWLEDGE);
 
        // Look up a JMS topic
        Topic chatTopic = (Topic)jndi.lookup(topicName);
 
        // Create a JMS publisher and subscriber
        TopicPublisher publisher = 
            pubSession.createPublisher(chatTopic);
        TopicSubscriber subscriber = 
            subSession.createSubscriber(chatTopic);
 
        // Set a JMS message listener
        subscriber.setMessageListener(this);
 
        // Intialize the Chat application
        set(connection, pubSession, subSession, publisher, username);
 
        // Start the JMS connection; allows messages to be delivered
        connection.start( );
 
    }
    /* Initialize the instance variables */
    public void set(TopicConnection con, TopicSession pubSess,
                    TopicSession subSess, TopicPublisher pub, 
                    String username) {
        this.connection = con;
        this.pubSession = pubSess;
        this.subSession = subSess;
        this.publisher = pub;
        this.username = username;
    }
    /* Receive message from topic subscriber */
    public void onMessage(Message message) {
        try {
            TextMessage textMessage = (TextMessage) message;
            String text = textMessage.getText( );
            System.out.println(text);
        } catch (JMSException jmse){ jmse.printStackTrace( ); }
    }
    /* Create and send message using topic publisher */
    protected void writeMessage(String text) throws JMSException {
        TextMessage message = pubSession.createTextMessage( );
        message.setText(username+" : "+text);
        publisher.publish(message);
    }
    /* Close the JMS connection */
    public void close( ) throws JMSException {
        connection.close( );
    }
    /* Run the Chat client */
    public static void main(String [] args){
        try{
            if (args.length!=3)
                System.out.println("Topic or username missing");
 
            // args[0]=topicName; args[1]=username; args[2]=password
            Chat chat = new Chat(args[0],args[1],args[2]);
 
            // Read from command line
            BufferedReader commandLine = new 
              java.io.BufferedReader(new InputStreamReader(System.in));
 
            // Loop until the word "exit" is typed
            while(true){
                String s = commandLine.readLine( );
                if (s.equalsIgnoreCase("exit")){
                    chat.close( ); // close down connection
                    System.exit(0);// exit program
                } else 
                    chat.writeMessage(s);
            }
        } catch (Exception e){ e.printStackTrace( ); }
    }
}