Java Message Service Pub/sub 编程

文章来源（IBM中国）

相同又不同

下面有这两个 pub/sub 程序——TPublisher.java 的代码清单 和 TSubscriber.java 的代码清单。我们不再像对 PTP 程序那样一步一步地去分析它们，因为除了所使用的 JMS 接口之外，它们与 QSender.java 和 QReceiver.java 是完全一样的。

在运行这些程序之前需要设置管理对象 TopicConnectionFactory 和 Topic。

运行后将会看到它们与 PTP 程序的不同。如果用同样的 QueueConnectionFactory 和 Queue 运行 QReceiver 的多个实例，您会看到在用 QSender 发送消息时，一个 QReceiver 实例只接收一个发送消息。

如果运行 TSubscriber 的多个实例，那么您就会看到从 TPublisher 发送的所有消息是由 TSubscriber 的所有实例接收的。

TPublisher.java 的代码清单

import java.io.*;
import javax.jms.*;
import javax.naming.*;

public class TPublisher {

    public static void main(String[] args) {

        new TPublisher().publish();
    }

    public void publish() {

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        try {
            //Prompt for JNDI names
            System.out.println("Enter TopicConnectionFactory name:");
            String factoryName = reader.readLine();
            System.out.println("Enter Topic name:");
            String topicName = reader.readLine();

            //Look up administered objects
            InitialContext initContext = new InitialContext();
            TopicConnectionFactory factory =
                (TopicConnectionFactory) initContext.lookup(factoryName);
            Topic topic = (Topic) initContext.lookup(topicName);
            initContext.close();

            //Create JMS objects
            TopicConnection connection = factory.createTopicConnection();
            TopicSession session =
                connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);
            TopicPublisher publisher = session.createPublisher(topic);

            //Send messages
            String messageText = null;
            while (true) {
                System.out.println("Enter message to send or 'quit':");
                messageText = reader.readLine();
                if ("quit".equals(messageText))
                    break;
                TextMessage message = session.createTextMessage(messageText);
                publisher.publish(message);
            }

            //Exit
            System.out.println("Exiting...");
            reader.close();
            connection.close();
            System.out.println("Goodbye!");

        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
    }
}

TSubscriber.java 的代码清单

import java.io.*;
import javax.jms.*;
import javax.naming.*;

public class TSubscriber implements MessageListener {

    private boolean stop = false;

    public static void main(String[] args) {

        new TSubscriber().subscribe();
    }

    public void subscribe() {

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        try {
            //Prompt for JNDI names
            System.out.println("Enter TopicConnectionFactory name:");
            String factoryName = reader.readLine();
            System.out.println("Enter Topic name:");
            String topicName = reader.readLine();
            reader.close();

            //Look up administered objects
            InitialContext initContext = new InitialContext();
            TopicConnectionFactory factory =
                (TopicConnectionFactory) initContext.lookup(factoryName);
            Topic topic = (Topic) initContext.lookup(topicName);
            initContext.close();

            //Create JMS objects
            TopicConnection connection = factory.createTopicConnection();
            TopicSession session =
                connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);
            TopicSubscriber subscriber = session.createSubscriber(topic);
            subscriber.setMessageListener(this);
            connection.start();

            //Wait for stop
            while (!stop) {
                Thread.sleep(1000);
            }

            //Exit
            System.out.println("Exiting...");
            connection.close();
            System.out.println("Goodbye!");

        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void onMessage(Message message) {

        try {
            String msgText = ((TextMessage) message).getText();
            System.out.println(msgText);
            if ("stop".equals(msgText))
                stop = true;
        } catch (JMSException e) {
            e.printStackTrace();
            stop = true;
        }
    }
}