前面的例子中創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的格式是類似於SQL-92的一種語法。可以用來比較消息頭信息和屬性。
下面的例子中，創建兩個消費者，共同監聽同一個Queue，但是它們的Selector不同，然后創建一個消息生產者，來發送多個消息。
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。