jms topic与jms queue区别

在JMS中，Topic实现publish和subscribe语义。一条消息被publish时，它将发到所有感兴趣的订阅者，所以零到多个 subscriber将接收到消息的一个拷贝。但是在消息代理接收到消息时，只有激活订阅的subscriber能够获得消息的一个拷贝。

JMS Queue执行load balancer语义。一条消息仅能被一个consumer收到。如果在message发送的时候没有可用的consumer，那么它将被保存一直到能处 理该message的consumer可用。如果一个consumer收到一条message后却不响应它，那么这条消息将被转到另一个consumer 那儿。一个Queue可以有很多consumer，并且在多个可用的consumer中负载均衡

Jms规范里的两种message传输方式Topic和Queue，两者的对比如下表()：

	Topic	Queue
概要	Publish Subscribe messaging 发布订阅消息	Point-to-Point 点对点
有无状态	topic数据默认不落地，是无状态的。	Queue数据默认会在mq服务器上以文件形式保存，比如Active MQ一般保存在$AMQ_HOME\data\kr-store\data下面。也可以配置成DB存储。
完整性保障	并不保证publisher发布的每条数据，Subscriber都能接受到。	Queue保证每条数据都能被receiver接收。
消息是否会丢失	一般来说publisher发布消息到某一个topic时，只有正在监听该topic地址的sub能够接收到消息；如果没有sub在监听，该topic就丢失了。	Sender发送消息到目标Queue，receiver可以异步接收这个Queue上的消息。Queue上的消息如果暂时没有receiver来取，也不会丢失。
消息发布接收策略	一对多的消息发布接收策略，监听同一个topic地址的多个sub都能收到publisher发送的消息。Sub接收完通知mq服务器	一对一的消息发布接收策略，一个sender发送的消息，只能有一个receiver接收。receiver接收完后，通知mq服务器已接收，mq服务器对queue里的消息采取删除或其他操作。

以下是符合Jms1.1规范的使用Queue传输消息的代码，使用Active mq作为Jms的实现，想要更clean的代码，可以考虑将Amq的实现DI：

public   void  testMySend()  throws  JMSException {
        Connection connection = new  ActiveMQConnectionFactory( "admin" , "admin" , "tcp://localhost:61616" ).createConnection();
            Session session = null ;
            Queue queue = null ;
            MessageProducer producer = null ;
            session = connection.createSession(false , Session.AUTO_ACKNOWLEDGE);
            queue=session.createQueue("myTest" );
            producer= session.createProducer(queue);
            Message msg=session.createTextMessage("hello" );
            producer.send(msg);
            producer.close();
            session.close();
            connection.close();
    }

    public   void  testMyReceive()  throws  JMSException{
        Connection connection = new  ActiveMQConnectionFactory( "admin" , "admin" , "tcp://localhost:61616" ).createConnection();
        Session session = connection.createSession(false , Session.AUTO_ACKNOWLEDGE);
        Queue queue = session.createQueue("myTest" );
        MessageConsumer consumer= session.createConsumer(queue);
        consumer.setMessageListener(new  MyListener());
        connection.start();
        consumer.close();
        session.close();
            connection.close();
    }

public void testMySend() throws JMSException {
        Connection connection = new ActiveMQConnectionFactory("admin","admin","tcp://localhost:61616").createConnection();
            Session session = null;
            Queue queue = null;
            MessageProducer producer = null;
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
            queue=session.createQueue("myTest");
            producer= session.createProducer(queue);
            Message msg=session.createTextMessage("hello");
            producer.send(msg);
            producer.close();
            session.close();
            connection.close();
    }

    public void testMyReceive() throws JMSException{
        Connection connection = new ActiveMQConnectionFactory("admin","admin","tcp://localhost:61616").createConnection();
        Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
        Queue queue = session.createQueue("myTest");
        MessageConsumer consumer= session.createConsumer(queue);
        consumer.setMessageListener(new MyListener());
        connection.start();
        consumer.close();
        session.close();
            connection.close();
    }

消费端需要设定一个MessageListener：

private   class  MyListener  implements  MessageListener{
        public   void  onMessage(Message message) {
        System.out.println("msg start!----------------" );
        try  {
            System.out.println("" +((TextMessage)message).getText());
        } catch  (JMSException e) {
            e.printStackTrace();
        }
        System.out.println("msg end!----------------" );
        }
    }

以下是符合Jms1.1规范的使用Topic 发送消息的代码：

public   void  testMyTopicPublisher()  throws  JMSException {
         Connection connection = new  ActiveMQConnectionFactory( "admin" , "admin" , "tcp://localhost:61616" ).createConnection();
            Session session = null ;
            Topic topic = null ;
            MessageProducer producer = null ;
            session = connection.createSession(false , Session.AUTO_ACKNOWLEDGE);
            topic=session.createTopic("myTopicTest" );
            producer= session.createProducer(topic);
            producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
            Message msg=session.createTextMessage("hello and whatever u say" );
            producer.send(msg);
            producer.close();
            session.close();
            connection.close();
    }

public void testMyTopicPublisher() throws JMSException {
         Connection connection = new ActiveMQConnectionFactory("admin","admin","tcp://localhost:61616").createConnection();
            Session session = null;
            Topic topic = null;
            MessageProducer producer = null;
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
            topic=session.createTopic("myTopicTest");
            producer= session.createProducer(topic);
            producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
            Message msg=session.createTextMessage("hello and whatever u say");
            producer.send(msg);
            producer.close();
            session.close();
            connection.close();
    }

以下是符合Jms1.1规范的使用Topic 接收消息的代码：

public   static   void  testMyTopicConsumer()  throws  JMSException, InterruptedException{
        Connection connection = new  ActiveMQConnectionFactory( "admin" , "admin" , "tcp://localhost:61616" ).createConnection();
         Session session = connection.createSession(false , Session.CLIENT_ACKNOWLEDGE);
         Topic topic = session.createTopic("myTopicTest" );
         MessageConsumer consumer= session.createConsumer(topic);
         consumer.setMessageListener(new  MyListener());
         connection.start();
    }

public static void testMyTopicConsumer() throws JMSException, InterruptedException{
        Connection connection = new ActiveMQConnectionFactory("admin","admin","tcp://localhost:61616").createConnection();
         Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
         Topic topic = session.createTopic("myTopicTest");
         MessageConsumer consumer= session.createConsumer(topic);
         consumer.setMessageListener(new MyListener());
         connection.start();
    }

jms在创建Session时可以有两个参数，第一个参数是是否使用事务，第二个参数是消费者向发送者确认消息已经接收的方式：

Session session = connection.createSession( false , Session.CLIENT_ACKNOWLEDGE);

Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);

确认消息的方式有如下三种：

AUTO_ACKNOWLEDGE(自动通知)

CLIENT_ACKNOWLEDGE(客户端自行决定通知时机)

DUPS_OK_ACKNOWLEDGE(延时//批量通知)

如果使用的是 客户端自行决定通知时机 方式，那么需要在MessageListener里显式调用message.acknowledge()来通知服务器。服务器接收到通知后采取相应的操作。