RabbitMQ之三 Publish/Subscribe

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