深入掌握JMS（九）：Selector

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。

 

下面的例子中，创建两个消费者，共同监听同一个Queue，但是它们的Selector不同，然后创建一个消息生产者，来发送多个消息。

 

 

import javax.jms.Connection;import javax.jms.JMSException;import javax.jms.Message;import javax.jms.MessageConsumer;import javax.jms.MessageListener;import javax.jms.MessageProducer;import javax.jms.Queue;import javax.jms.Session;import javax.jms.TextMessage;import org.apache.activemq.ActiveMQConnectionFactory;import org.apache.activemq.command.ActiveMQQueue;public class JMSSelectorTest {public static void main(String[] args) throws Exception {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。