rabbitmq学习3:Publish/Subscribe-优快云博客

本文详细介绍了Publish/Subscribe模式的基本概念，并通过代码实例展示了如何在RabbitMQ中实现这一模式，包括Exchange的类型选择、发布消息及绑定Queue的过程。通过两个C端程序实例，演示了如何利用不同Queue接收相同的消息，最终实现消息均匀分发到所有消费者。

在前面的Work Queue中的消息是均匀分配消息给消费者；如果我想把消息分发给所有的消费者呢？那应当怎么操作呢？这就是要下面提到的Publish/Subscribe（分布/订阅）。让我们开始Publish/Subscribe之旅吧!

Publish/Subscribe的工作示意图如下：

在上图中的X表示Exchange(交换区);Exchange的类型有：direct , topic , headers 和 fanout

Publish/Subscribe的Exchang的类型为fanout;声明Publish/Subscribe的Exchang代码如下：

channel.exchangeDeclare("logs", "fanout");

对于Work Queue中提到的发布消息的代码如下：

channel.basicPublish("", queueName,   null, message.getBytes());

但对于Publish/Subscribe中发布消息中的Queue的使用的是默认的；代码如下：

channel.basicPublish( "logs", "", null, message.getBytes());

Exchange和各Queue之间是如何通信的呢？主要是通过把Exchange和各Queue绑定（binding）；示意代码如下:

channel.queueBind(queueName, exchangeName, "");

Publish/Subscribe加入绑定的工作示意图如下：

那我们就开始程序代码吧：P端的代码如下：

package com.abin.rabbitmq;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;

public class EmitLog {
	private static final String EXCHANGE_NAME = "logs";

	public static void main(String[] argv) throws Exception {
		ConnectionFactory factory = new ConnectionFactory();
		factory.setHost("localhost");
		Connection connection = factory.newConnection();
		Channel channel = connection.createChannel();
		channel.exchangeDeclare(EXCHANGE_NAME, "fanout");//声明Exchange
		for (int i = 0; i <= 2; i++) {
			String message = "hello word!" + i;
			channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes());
			System.out.println(" [x] Sent '" + message + "'");
		}
		channel.close();
		connection.close();
	}

}

运行结果如下：

 [x] Sent 'hello word!0'
 [x] Sent 'hello word!1'
 [x] Sent 'hello word!2'

C端的代码如下：

package com.abin.rabbitmq;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;

public class ReceiveLogsOne {
	private static final String EXCHANGE_NAME = "logs";

	public static void main(String[] argv) throws Exception {
		ConnectionFactory factory = new ConnectionFactory();
		factory.setHost("localhost");
		Connection connection = factory.newConnection();
		Channel channel = connection.createChannel();
		channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
		String queueName = "log-fb1";
		channel.queueDeclare(queueName, false, false, false, null);
		channel.queueBind(queueName, EXCHANGE_NAME, "");//把Queue、Exchange绑定
		QueueingConsumer consumer = new QueueingConsumer(channel);
		channel.basicConsume(queueName, true, consumer);
		while (true) {
			QueueingConsumer.Delivery delivery = consumer.nextDelivery();
			String message = new String(delivery.getBody());
			System.out.println(" [x] Received '" + message + "'");
		}
	}
}

对于C端的代码我写了二个差不多的程序，只需要修改一下queueName。这样就形成了二个Queue;运行结果相同；

运行结果可能如下：

 [x] Received 'hello word!0'
 [x] Received 'hello word!1'
 [x] Received 'hello word!2'