ActiveMQ学习系列（二）----生产者客户端（java）

上文主要简单地将activeMq搭建了起来，并且可以用web console去登录查看相关的后台功能。

本文将学习如何用java语言实现一个生产者客户端，主要参考了以下链接：

http://activemq.apache.org/jndi-support.html

代码已上传github，建议先下载下来实际运行一遍：

https://github.com/cctvckl/big-data-learning/tree/master/activemq-learning

一、ActiveMq支持的协议

ActiveMq作为消息中间件，支持多种连接协议，如：tcp、amqp、stomp、mqtt等。

如果启动时以./activemq console方式启动，可以看到如下输出：

而下文将要讲解的java客户端程序，就是基于其中的tcp协议。

将tcp://host:port这个地址记录下来，下面需要用到。

二、大体思路

1、本地配置文件，配置要连接的ActiveMq服务器、包括连接协议和端口号，配置要发送消息的目标队列、目标topic等等。

2、程序读取上述配置文件，生成连接会话、生成消息生产者、发送消息、关闭连接。
三、具体步骤

1、配置文件样例：

java.naming.factory.initial = org.apache.activemq.jndi.ActiveMQInitialContextFactory

# Use the following property to configure the default connector
java.naming.provider.url = tcp://192.168.2.140:61616

# Use the following property to specify the JNDI name the connection factory
# should appear as.
connectionFactoryNames = ConnectionFactory, queueConnectionFactory, topicConnectionFactry

# Register some queues in JNDI using the form:
#   queue.[jndiName] = [physicalName]
queue.MyQueue = example.MyQueue

# Register some topics in JNDI using the form:
#   topic.[jndiName] = [physicalName]
topic.MyTopic = example.MyTopic

释义：上面的url项要与第一章节里面的那个地址匹配；

topic.MyTopic中的点号分割开的第二部分（此例为MyTopic）会被注册为JNDI名, 至于value（example.MyTopic）为topic名，在Web Console可以看到。

queue.MyQueue同理。

2、配置文件完毕，下面介绍业务代码：

package com.ckl.activemq;
/**
 * The SimpleQueueSender class consists only of a main method,
 * which sends several messages to a queue.
 *
 * Run this program in conjunction with SimpleQueueReceiver.
 * Specify a queue name on the command line when you run the
 * program.  By default, the program sends one message.  Specify
 * a number after the queue name to send that number of messages.
 */

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.jms.*;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

/**
 * A simple polymorphic JMS producer which can work with Queues or Topics which
 * uses JNDI to lookup the JMS connection factory and destination.
 */
public class SimpleProducer {
    private static final Logger LOG = LoggerFactory.getLogger(SimpleProducer.class);

    private SimpleProducer() {}

    /**
     * @param args the destination name to send to and optionally, the number of
     *                messages to send
     */
    public static void main(String[] args) {
        Context jndiContext = null;
        ConnectionFactory connectionFactory = null;
        Connection connection = null;
        Session session = null;
        Destination destination = null;
        MessageProducer producer = null;
        String destinationName = null;
        final int numMsgs;
　　　　//这边被我手动修改了，比较不喜欢每次运行时还要修改Run configuration，麻烦。
        args = new String[2];
        args[0] = "MyTopic";
        args[1] = "3";

        if ((args.length < 1) || (args.length > 2)) {
            LOG.info("Usage: java SimpleProducer <destination-name> [<number-of-messages>]");
            System.exit(1);
        }

        destinationName = args[0];
        LOG.info("Destination name is " + destinationName);

        if (args.length == 2) {
            numMsgs = (new Integer(args[1])).intValue();
        }
        else {
            numMsgs = 1;
        }

        /*
         * Create a JNDI API InitialContext object
         */
        try {
            jndiContext = new InitialContext();
        }
        catch (NamingException e) {
            LOG.info("Could not create JNDI API context: " + e.toString());
            System.exit(1);
        }

        /*
         * Look up connection factory and destination.
         */
        try {
            connectionFactory = (ConnectionFactory)jndiContext.lookup("ConnectionFactory");
            destination = (Destination)jndiContext.lookup(destinationName);
        }
        catch (NamingException e) {
            LOG.info("JNDI API lookup failed: " + e);
            System.exit(1);
        }

        /*
         * Create connection. Create session from connection; false means
         * session is not transacted. Create sender and text message. Send
         * messages, varying text slightly. Send end-of-messages message.
         * Finally, close the connection.
         */
        try {
            connection = connectionFactory.createConnection();
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
            producer = session.createProducer(destination);
            TextMessage message = session.createTextMessage();

            for (int i = 0; i < numMsgs; i++) {
                message.setText("This is message " + (i + 1));
                LOG.info("Sending message: " + message.getText());
                producer.send(message);
            }

            /*
             * Send a non-text control message indicating end of messages.
             */
            producer.send(session.createMessage());
        }
        catch (JMSException e) {
            LOG.info("Exception occurred: " + e);
        }
        finally {
　　　　　　　//睡眠是我手动加的，主要为了观察效果
            try {
                Thread.sleep(100000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            if (connection != null) {
                try {
                    connection.close();
                }
                catch (JMSException ignored) {}
            }
        }
    }
}

代码不难理解：jndi读取配置文件，建立连接，发消息，关闭连接。

运行结果：

此时查看Web Console，

可以看到来自客户端的连接信息。

本例子就先到这里，详细还请参考贴的代码链接和官网文档。

欢迎留言交流。