在创建一个Consumer的时候,Session接口还提供了另一个方法:
MessageConsumer createConsumer(Destination destination, java.lang.String messageSelector)
//Creates a MessageConsumer for the specified destination, using a message selector.
这里messageSelector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。
messageSelector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。
使用示例:
在上面的示例中,创建了一个指定messageSelector的Consumer。当Producer发送消息时,会在消息Header中设置不同的消息属性。Consumer根据messageSelector表达式选择拥有指定属性的消息进行处理。
package com.gof.jms.test;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.DeliveryMode;
import javax.jms.Destination;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageListener;
import javax.jms.MessageProducer;
import javax.jms.Session;
import javax.jms.TextMessage;
import org.apache.activemq.ActiveMQConnectionFactory;
public class JMSSelectorTest {
public static final String user = "system";
public static final String password = "manager";
public static final String url = "tcp://localhost:61616";
public static final String queueName = "test_queue";
public static final String messageBody = "Hello Asynchronous JMS!";
public static final boolean transacted = false;
public static final boolean persistent = false;
public static void main(String[] args){
Connection connection = null;
Session session = null;
try{
// create the connection
ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(user, password, url);
connection = connectionFactory.createConnection();
connection.start();
// create the session
session = connection.createSession(transacted, Session.AUTO_ACKNOWLEDGE);
Destination destination = session.createQueue(queueName);
// create the producer
MessageProducer producer = session.createProducer(destination);
if (persistent){
producer.setDeliveryMode(DeliveryMode.PERSISTENT);
}else{
producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
}
// create text message
for (int i =0; i < 10; i++){
Message message = session.createTextMessage(messageBody + " " + Integer.toString(i));
String selectorStr = ((i+1) % 2 == 0) ? "myselector":"yourselector";
message.setStringProperty("selector", selectorStr);
// send the message
producer.send(message);
System.out.println("Send message with string property selector =" + selectorStr +" : " + ((TextMessage)message).getText());
}
// create the consumer with the selector expression
MessageConsumer consumer = session.createConsumer(destination, "selector='myselector'");
consumer.setMessageListener(new MessageListener() {
public void onMessage(Message message) {
// TODO Auto-generated method stub
TextMessage recvMessage = (TextMessage)message;
try{
System.out.println("Receive message: " + recvMessage.getText());
}catch (JMSException e){
e.printStackTrace();
}
}
});
// To avoid the connection closed before the message listener received the message.
Thread.sleep(5000);
}catch (Exception e){
e.printStackTrace();
}finally{
try{
// close session and connection
if (session != null){
session.close();
}
if (connection != null){
connection.close();
}
}catch (Exception e){
e.printStackTrace();
}
}
}
}
执行的结果如下:
Send message with string property selector =yourselector : Hello Asynchronous JMS! 0
Send message with string property selector =myselector : Hello Asynchronous JMS! 1
Send message with string property selector =yourselector : Hello Asynchronous JMS! 2
Send message with string property selector =myselector : Hello Asynchronous JMS! 3
Send message with string property selector =yourselector : Hello Asynchronous JMS! 4
Send message with string property selector =myselector : Hello Asynchronous JMS! 5
Send message with string property selector =yourselector : Hello Asynchronous JMS! 6
Send message with string property selector =myselector : Hello Asynchronous JMS! 7
Send message with string property selector =yourselector : Hello Asynchronous JMS! 8
Send message with string property selector =myselector : Hello Asynchronous JMS! 9
Receive message: Hello Asynchronous JMS! 1
Receive message: Hello Asynchronous JMS! 3
Receive message: Hello Asynchronous JMS! 5
Receive message: Hello Asynchronous JMS! 7
Receive message: Hello Asynchronous JMS! 9
只有设置了消息头属性“selector”为“myselector”的消息才会被Consumer接收到。