RabbitMQ之三 Publish/Subscribe

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/nongfuyumin/article/details/78689742

在上篇文章Work Quene中我们创建了一个Work Queue，在Work Queue中的每个task会准确的分发给worker，这边文章中，我们需要将一个消息分发给多个consumers，这个模式称为发布订阅 "publish/subscribe"

为了举例说明发布订阅模式，我们构建一个简单的日志系统，包含两部分，一部分用于发布日志，另一部分用于接收并打印日志。

在我们的日志系统中，发布日志意味着将日志消息"广播"给所有的订阅者。

交换机Exchanges

首先介绍下RabbitMQ的消息模型，RabbitMQ中的Producer不会直接向queue发送消息，实际上，很多Producer不清楚消息将被分发到哪个queue，相反，Producer只能把消息发送到交换机(exchange)，交换机连接着Producer和queue，一方面交换机从Producer中接收数据，另一方面交换机往queue中放数据，所以交换机必须清楚怎么处理接收到的消息，是应该添加到一个queue，还是应该添加到多个queues，或者直接丢弃，这规则取决于exchange type 交换机的模型如下

exchange type有这几种：direct,topic,headers和fanout，首先来看下fanout这种类型

fanout exchange很简单，它将从producer接收到的数据直接广播给所有它知道的queue

消息模型如下：

我们的日志系统代码如下：

客户端：EmitLog.java

package org.rabbitmq;

import com.rabbitmq.client.BuiltinExchangeType;
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");
	    factory.setPort(5673);
	    Connection connection = factory.newConnection();
	    Channel channel = connection.createChannel();

	    channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.FANOUT);
	    
	    String message = getMessage( new String[]{"hello","how","are","you"});

	    channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes("UTF-8"));
	    System.out.println(" [x] Sent '" + message + "'");

	    channel.close();
	    connection.close();
	  }

	  private static String getMessage(String[] strings){
	    if (strings.length < 1)
	    	    return "info: Hello World!";
	    return joinStrings(strings, " ");
	  }

	  private static String joinStrings(String[] strings, String delimiter) {
	    int length = strings.length;
	    if (length == 0) return "";
	    StringBuilder words = new StringBuilder(strings[0]);
	    for (int i = 1; i < length; i++) {
	        words.append(delimiter).append(strings[i]);
	    }
	    return words.toString();
	  }
}

服务端ReceiveLogs.java

package org.rabbitmq;

import java.io.IOException;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Consumer;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;

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

	  public static void main(String[] argv) throws Exception {
	    ConnectionFactory factory = new ConnectionFactory();
	    factory.setHost("localhost");
	    factory.setPort(5673);
	    Connection connection = factory.newConnection();
	    Channel channel = connection.createChannel();

	    channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
	    String queueName = channel.queueDeclare().getQueue();
	    channel.queueBind(queueName, EXCHANGE_NAME, "");

	    System.out.println("Thread："+ Thread.currentThread().hashCode()+"[*] Waiting for messages. To exit press CTRL+C");

	    Consumer consumer = new DefaultConsumer(channel) {
	      @Override
	      public void handleDelivery(String consumerTag, Envelope envelope,
	                                 AMQP.BasicProperties properties, byte[] body) throws IOException {
	        String message = new String(body, "UTF-8");
	        System.out.println(" [x] Received '" + message + "'");
	      }
	    };
	    channel.basicConsume(queueName, true, consumer);
	  }
}

运行两次EmitLog，然后再运行ReceiveLogs，结果如下

结果显示从producer发送的消息，被两个consumer都接收到了。

参考：http://www.rabbitmq.com/tutorials/tutorial-three-java.html