JMS&MQ,从入门到精通(六)

以你之姓@ 2022-06-17 14:39 134阅读 0赞

本篇我们来介绍一下activeMq的Queue的细节之处
    
     前面的例子中创建一个消息消费者使用的是:
     sesssion.createConsumer(destination)另外，还提供了另一种方式：
     sesssion.createConsumer(destination, selector)这里selector是一个字符串，用来过滤消息。也就是说，这种方式可以创建一个可以只
     接收特定消息的一个消费者Selector的格式是类似于SQL-92的一种语法,可以用来比较消息头信息和属性

# 思路 #

1.创建两个消费者，共同监听同一个Queue,但是它们的Selector不同
    2.然后创建一个消息生产者，来发送多个消息

# 一个简单的实例 #

ActiveMQConnectionFactory factory = new ActiveMQConnectionFactory("vm://localhost");
    Connection connection = factory.createConnection();
    connection.start();
    
    Queue queue = new ActiveMQQueue("testQueue");
    
    Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
    
    MessageConsumer comsumerA = session.createConsumer(queue, "receiver = 'A'");
    comsumerA.setMessageListener(new MessageListener(){
        public void onMessage(Message m) {
            try {
                System.out.println("ConsumerA get " + ((TextMessage) m).getText());
            } catch (JMSException e1) { }
        }
    });
    
    MessageConsumer comsumerB = session.createConsumer(queue, "receiver = 'B'");
    comsumerB.setMessageListener(new MessageListener(){
        public void onMessage(Message m) {
            try {
                System.out.println("ConsumerB get " + ((TextMessage) m).getText());
            } catch (JMSException e) { }
        }
    });
    
    MessageProducer producer = session.createProducer(queue);
    for(int i=0; i<10; i++) {
        String receiver = (i%3 == 0 ? "A" : "B");
        TextMessage message = session.createTextMessage("Message" + i + ", receiver:" + receiver);
        message.setStringProperty("receiver", receiver);
        producer.send(message );
    }
    /** 结果如下： ConsumerA get Message0, receiver:A ConsumerB get Message1, receiver:B ConsumerB get Message2, receiver:B ConsumerA get Message3, receiver:A ConsumerB get Message4, receiver:B ConsumerB get Message5, receiver:B ConsumerA get Message6, receiver:A ConsumerB get Message7, receiver:B ConsumerB get Message8, receiver:B ConsumerA get Message9, receiver:A 可以看出，消息消费者只会取走它自己感兴趣的消息。 * */

不知道大家看出来了没,这里有点SQL-92标准的where查询的味道;

--------------------

> 关键代码

TextMessage message = session.createTextMessage("Message" + i + ", receiver:" + receiver);
    message.setStringProperty("receiver", receiver);

运行结果如下图;

![这里写图片描述][SouthEast]

下篇将结合本篇的精华之处,做一个复杂一点的实例,前方高能!!!

[SouthEast]: /images/20220617/c59a992ae9ee4292adc968ee98946f6d.png