深入掌握JMS（九）：Selector

moonboat 2009-07-12

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深入掌握JMS（九）：Selector

前面的例子中創(chuàng)建一個消息消費者使用的是:
          sesssion.createConsumer(destination)
另外，還提供了另一種方式：
    sesssion.createConsumer(destination, selector)
這里selector是一個字符串，用來過濾消息。也就是說，這種方式可以創(chuàng)建一個可以只接收特定消息的一個消費者。Selector的格式是類似于SQL-92的一種語法?？梢杂脕肀容^消息頭信息和屬性。

下面的例子中，創(chuàng)建兩個消費者，共同監(jiān)聽同一個Queue，但是它們的Selector不同，然后創(chuàng)建一個消息生產者，來發(fā)送多個消息。

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 );
        }
    }
}

結果如下：
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，消息消費者只會取走它自己感興趣的消息。