rabbitMQ学习笔记(2):最简单的helloworld

上一篇文章提到了rabbitMQ的体系结构和一些核心概念，这篇文章就通过一个最简单的Java版helloWorld实例来看实际代码中这些概念的体现。

前期准备

1、在自己的电脑上安装rabbitMQ server

2、下载rabbitMQ 的java API，就是一个jar包，并在工程中导入

introduction

上一篇说到MQ解决的主要问题是降低系统之间、模块之间的耦合度，在这个层面上，可以将rabbitMQ理解为一个message broker,producer将message发送给rabbitMQ，rabbitMQ做为中间方将message传递给consumer，从而使producer和consumer之间解耦。message在两者之间传递的时候可以依据相应的规则进行路由，缓存甚至持久化

producer可以简单理解为发送消息的程序，在本文的图像中以下图代表producer：

       

   queue是模块间通信的“信箱”，其生命周期只存在于rabbitMQ server中，本质而言，queue就是一个无穷缓冲队列，一个或者多个producer/consumer都可以无限制的连接上mq，这里说的无限制是在数量上而言，连接MQ server还是要遵循rabbitMQ各种语言的API的规定。在本文的图像中以下图代表queue：

consumer就是连接在MQ上等待传送过来进行消费的：

note:producer consumer 和queue不一定存在于同一台机器上，并且在大多数情况下是不在同一台机器上的。对于大型系统而言，各个模块很有可能部署在不同机器上，模块和模块之间的通信远比同一台机器上的模块之间通信复杂，在实际生产环境中运用MQ也会有各种各样的问题与挑战。

传递一个最简单的HelloWorld

这部分我们不去深究rabbitMQ java api的细节，仅仅实现一个简单的模型

producer将一个message发送到queue中，queue将message传递给consumer供其消费。在本篇的程序中consumer仅仅将message打印出来。

直接上代码

producer的代码：

public class Sender {private final static String QUEUE_NAME = "hello";  public static void main(String[] argv) throws Exception {    //create a connection to a server //  The connection abstracts the socket connection, and takes care of protocol version negotiation and //  authentication and so on for us. Here we connect to a broker on the local machine - hence the locallhost. //  If we wanted to connect to a broker on a different machine we'd simply specify its name or IP address here.ConnectionFactory factory = new ConnectionFactory();    factory.setHost("localhost");    Connection connection = factory.newConnection();//    Next we create a channel, which is where most of the API for getting things done resides.    Channel channel = connection.createChannel();//    To send, we must declare a queue for us to send to; then we can publish a message to the queue:    channel.queueDeclare(QUEUE_NAME, false, false, false, null);    String message = "Hello World!";    //publish the message to the queue    channel.basicPublish("", QUEUE_NAME, null, message.getBytes("UTF-8"));    System.out.println(" [x] Sent '" + message + "'");    channel.close();    connection.close();  }}

consumer的代码：

public class Receiver {private static final String QUEUE_NAME = "hello";private static final String HOST_ADDRESS = "localhost"; public static void main(String[] args) throws IOException, TimeoutException {//Setting up is the same as the sender; //we open a connection and a channel, and declare the queue from which we're going to consume. //Note this matches up with the queue that send publishes to.ConnectionFactory factory = new ConnectionFactory();factory.setHost(HOST_ADDRESS);Connection connection = factory.newConnection();Channel channel = connection.createChannel();//Note that we declare the queue here, as well. //Because we might start the receiver before the sender, //we want to make sure the queue exists before we try to consume messages from it.channel.queueDeclare(QUEUE_NAME, false, false, false, null);System.out.println("[*] waiting for message .To exit press CTRL+C");//We're about to tell the server to deliver us the messages from the queue. //Since it will push us messages asynchronously, we provide a callback in the form of an object that //will buffer the messages until we're ready to use them. That is what a DefaultConsumer subclass does.Consumer consumer = new DefaultConsumer(channel){@Overridepublic void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties, byte[] body)throws IOException {String message = new String(body,"UTF-8");System.out.println(" [x] Received '" + message + "'");}};channel.basicConsume(QUEUE_NAME,true, consumer);}}