activemq-topic

最新推荐文章于 2021-07-29 21:56:30 发布

最新推荐文章于 2021-07-29 21:56:30 发布 · 131 阅读

文章标签：

#mq #Publisher #subscriber

active-mq 专栏收录该内容

6 篇文章

订阅专栏

本文介绍了一种消息传递模式——发布/订阅模式，并通过具体的Java代码示例演示了如何实现消息的发布与订阅。该模式允许一个发布者发送消息给多个订阅者。文中还探讨了非持久订阅的概念，即客户端必须在线才能接收消息。

[url]http://wangxinchun.iteye.com/blog/2146172[/url]
[url]http://wangxinchun.iteye.com/blog/2146120[/url]
[url]http://wangxinchun.iteye.com/blog/2145998[/url]
[url]http://wangxinchun.iteye.com/blog/2145958[/url]
[url]http://wangxinchun.iteye.com/blog/2147335[/url]

[b]发布/订阅模式：针对一个发布者，多个订阅者都能接受到消息。[/b]

[b]非持久订阅：只有当客户端处于激活状态，也就是和JMS Provider 保持连接状态才能收到发送到某个主题的消息，而当客户端处于离线状态，这个时间段发到主题的消息将会丢失，永远不会收到。 [/b]
Publisher


/**
 *  消息发布*/
public class Publisher {
    private static final String BROKER_URL = "tcp://localhost:61616";
    private static final Boolean NON_TRANSACTED = false;
    private static final int NUM_MESSAGES_TO_SEND = 100;
    private static final long DELAY = 100;

    public static void main(String[] args) {
        String url = BROKER_URL;
        if (args.length > 0) {
            url = args[0].trim();
        }
        ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("admin", "password", url);
        Connection connection = null;

        try {

            connection = connectionFactory.createConnection();
            connection.start();

            Session session = connection.createSession(NON_TRANSACTED, Session.AUTO_ACKNOWLEDGE);
            Destination destination = session.createTopic("test-topic");
            MessageProducer producer = session.createProducer(destination);

            for (int i = 0; i < NUM_MESSAGES_TO_SEND; i++) {
                TextMessage message = session.createTextMessage("Message #" + i);
                System.out.println("Sending message #" + i);
                producer.send(message);
                Thread.sleep(DELAY);
            }

            // tell the subscribers we're done
            producer.send(session.createTextMessage("END"));

            producer.close();
            session.close();

        } catch (Exception e) {
            System.out.println("Caught exception!");
        }
        finally {
            if (connection != null) {
                try {
                    connection.close();
                } catch (JMSException e) {
                    System.out.println("Could not close an open connection...");
                }
            }
        }
    }
}

Subscriber


/**
 * 消息订阅*/
public class Subscriber implements MessageListener {
    private static final String BROKER_URL = "tcp://localhost:61616";
    private static final Boolean NON_TRANSACTED = false;

    private final CountDownLatch countDownLatch;
    public Subscriber(CountDownLatch latch) {
        countDownLatch = latch;
    }

    public static void main(String[] args) {
        String url = BROKER_URL;
        if (args.length > 0) {
            url = args[0].trim();
        }
        System.out.println("\nWaiting to receive messages... Either waiting for END message or press Ctrl+C to exit");
        ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("admin", "password", url);
        Connection connection = null;
        final CountDownLatch latch = new CountDownLatch(1);

        try {

            connection = connectionFactory.createConnection();
            connection.start();

            Session session = connection.createSession(NON_TRANSACTED, Session.AUTO_ACKNOWLEDGE);
            Destination destination = session.createTopic("test-topic");

            MessageConsumer consumer = session.createConsumer(destination);
            consumer.setMessageListener(new Subscriber(latch));

            latch.await();
            consumer.close();
            session.close();

        } catch (Exception e) {
            System.out.println("Caught exception!");
        }
        finally {
            if (connection != null) {
                try {
                    connection.close();
                } catch (JMSException e) {
                    System.out.println("Could not close an open connection...");
                }
            }
        }
    }

    @Override
    public void onMessage(Message message) {
        try {
            if (message instanceof TextMessage) {
                String text = ((TextMessage) message).getText();
                if ("END".equalsIgnoreCase(text)) {
                    System.out.println("Received END message!");
                    countDownLatch.countDown();
                }
                else {
                    System.out.println("Received message:" +text);
                }
            }
        } catch (JMSException e) {
            System.out.println("Got a JMS Exception!");
        }
    }
}

测试：
1、启动两个 Subscriber 然后启动一个 Publisher
结果：两个Subscriber 都收到了消息。

2、启动Publisher ，然后再启动 Subscriber
结果：Publisher发的消息，在 Publisher启动结束和 Subscriber启动结束之间的发送，全部丢失