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){
@Override
public 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);
}
}