最近需要用到activemq的topic发布订阅功能
activemq可以到官网下载，下载完成后启动很简单，bin/activemq start
到时候可以访问管理控制台，密码是admin/admin,
http://192.168.91.128:8161/admin/topics.jsp, 128是我的部署activemq的ip地址，用的是redhat6.4
mq broker搭建好之后，我们首先需要开发publish程序，这里我们通过tomcat的jndi来完成，
新建一个web项目，然后META-INF里面创建context.xml，内容如下，
<Context antiJARLocking="true">
<Resource
name="jms/ConnectionFactory"
auth="Container"
type="org.apache.activemq.ActiveMQConnectionFactory"
description="JMS Connection Factory"
factory="org.apache.activemq.jndi.JNDIReferenceFactory"
brokerURL="tcp://192.168.91.128:61616"
brokerName="LocalActiveMQBroker"
useEmbeddedBroker="false"/>
<Resource name="jms/topic/MyTopic"
auth="Container"
type="org.apache.activemq.command.ActiveMQTopic"
factory="org.apache.activemq.jndi.JNDIReferenceFactory"
physicalName="MY.TEST.FOO"/>
</Context>
完成之后写个servlet来获取jnid中配置的factory和topic信息，代码如下
InitialContext initCtx = new InitialContext();
Context envContext = (Context) initCtx.lookup("java:comp/env");
ConnectionFactory connectionFactory = (ConnectionFactory) envContext.lookup("jms/ConnectionFactory");
Connection connection = connectionFactory.createConnection();
Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
MessageProducer producer = session.createProducer((Destination) envContext.lookup("jms/topic/MyTopic"));
Message testMessage = session.createMessage();
testMessage.setStringProperty("testKey", "testValue111");
producer.send(testMessage);
deploy应用之前，需要将activemq-all-5.9.0.jar放入到tomcat/lib下面，启动tomcat，接着部署刚才的 servlet应用，启动tomcat后topic不会被自动创建，然后可以访问这个servlet，会发现topic会被创建，可以观察控制台
接着是消费者subscriber，
下面是普通的main方法来消费topic
package com.activemqtest;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import org.apache.activemq.ActiveMQConnectionFactory;
public class Reciever {
protected Topic queue;
protected String queueName = "MY.TEST.FOO";
protected String url = "tcp://192.168.91.128:61616";
protected int ackMode = Session.AUTO_ACKNOWLEDGE;
public static void main(String[] args) {
Reciever rec = new Reciever();
try {
rec.run();
} catch (Exception e) {
e.printStackTrace();
}
}
public void run() throws JMSException {
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
url);
TopicConnection connection = (TopicConnection) connectionFactory
.createTopicConnection();
connection.start();
MessageConsumer consumer = null;
Session session = connection.createTopicSession(false,
Session.AUTO_ACKNOWLEDGE);
queue = session.createTopic(queueName);
consumer = session.createConsumer(queue);
System.out.println(" Waiting for message (max 5) ");
for (int i = 0; i < 3; i++) {
Message message = consumer.receive();
processMessage(message);
}
System.out.println("Closing connection");
consumer.close();
session.close();
connection.close();
}
public void processMessage(Message message) {
try {
if (message instanceof TextMessage) {
TextMessage textMessage = (TextMessage) message;
String text = textMessage.getText();
System.out.println("Received: " + text);
} else {
System.out.println(message.getStringProperty("testKey"));
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
总结：
Topics
In JMS a Topic implements publish and subscribe semantics. When you publish a message it goes to all the subscribers who are interested - so zero to many subscribers will receive a copy of the message. Only subscribers who had an active subscription at the time the broker receives the message will get a copy of the message.
可以发现topic的消费者需要active，你不能等到publish完成之后，你启动subscriber，这样是接受不到消息的，但是queue的话不一样，不一定active才可以接受消息
另外有个问题是，tomcat只是一个servlet容器，并没有实现很多的j2ee标准比如jms，所以里面是没有javax.jms下面这些package的，需要单独下载J2ee.jar