RabbitMQ学习第三记：发布/订阅模式（Publish/Subscribe）

　　工作队列模式是直接在生产者与消费者里声明好一个队列，这种情况下消息只会对应同类型的消费者。

　　举个用户注册的列子：用户在注册完后一般都会发送消息通知用户注册成功（失败）。如果在一个系统中，用户注册信息有邮箱、手机号，那么在注册完后会向邮箱和手机号都发送注册完成信息。利用MQ实现业务异步处理，如果是用工作队列的话，就会声明一个注册信息队列。注册完成之后生产者会向队列提交一条注册数据，消费者取出数据同时向邮箱以及手机号发送两条消息。但是实际上邮箱和手机号信息发送实际上是不同的业务逻辑，不应该放在一块处理。这个时候就可以利用发布/订阅模式将消息发送到转换机（EXCHANGE），声明两个不同的队列（邮箱、手机），并绑定到交换机。这样生产者只需要发布一次消息，两个队列都会接收到消息发给对应的消费者。

1、什么是发布/订阅模式（Publish/Subscribe）

　　简单解释就是，可以将消息发送给不同类型的消费者。做到发布一次，消费多个。下图取自于官方网站（RabbitMQ）的发布/订阅模式的图例

P：消息的生产者

X：交换机

红色：队列

C1，C2：消息消费者

下面是利用用户注册解释的该模式。（先运行两个消费者，在运行生产者。如果没有提前将队列绑定到交换机，那么直接运行生产者的话，消息是不会发到任何队列里的）

2、生产者（Send）代码

public class Send
{
    private final static String EXCHANGE_NAME = "test_exchange_fanout";
    
    public static void main(String[] args)
    {
        try
        {
            //获取连接
            Connection connection = ConnectionUtil.getConnection();
            //从连接中获取一个通道
            Channel channel = connection.createChannel();
            //声明交换机（分发:发布/订阅模式）
            channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
            //发送消息
            for (int i = 0; i < 10; i++)
            {
                String message = "this is user registe message" + i;
                System.out.println("[send]：" + message);
                //发送消息
                channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes("utf-8"));
                Thread.sleep(5 * i);
            }
            channel.close();
            connection.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

运行结果：

[send]：this is user registe message0
[send]：this is user registe message1
[send]：this is user registe message2
[send]：this is user registe message3
[send]：this is user registe message4
[send]：this is user registe message5
[send]：this is user registe message6
[send]：this is user registe message7
[send]：this is user registe message8
[send]：this is user registe message9

3、消费者1（ReceiveEmail）

public class ReceiveEmail
{
    //交换机名称
    private final static String EXCHANGE_NAME = "test_exchange_fanout";
    
    //队列名称
    private static final String QUEUE_NAME    = "test_queue_email";
    
    public static void main(String[] args)
    {
        try
        {
            
            //获取连接
            Connection connection = ConnectionUtil.getConnection();
            //从连接中获取一个通道
            final Channel channel = connection.createChannel();
            //声明交换机（分发:发布/订阅模式）
            channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
            //声明队列
            channel.queueDeclare(QUEUE_NAME, false, false, false, null);
            //将队列绑定到交换机
            channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "");
            //保证一次只分发一个  
            int prefetchCount = 1;
            channel.basicQos(prefetchCount);
            //定义消费者
            DefaultConsumer consumer = new DefaultConsumer(channel)
            {
                //当消息到达时执行回调方法
                @Override
                public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties,
                        byte[] body) throws IOException
                {
                    String message = new String(body, "utf-8");
                    System.out.println("[email] Receive message：" + message);
                    try
                    {
                        //消费者休息2s处理业务
                        Thread.sleep(1000);
                    }
                    catch (InterruptedException e)
                    {
                        e.printStackTrace();
                    }
                    finally
                    {
                        System.out.println("[1] done");
                        //手动应答
                        channel.basicAck(envelope.getDeliveryTag(), false);
                    }
                }
            };
            //设置手动应答
            boolean autoAck = false;
            //监听队列
            channel.basicConsume(QUEUE_NAME, autoAck, consumer);
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    
}

运行结果：
[email] Receive message：this is user registe message0
[1] done
[email] Receive message：this is user registe message1
[1] done
[email] Receive message：this is user registe message2
[1] done
[email] Receive message：this is user registe message3
[1] done
[email] Receive message：this is user registe message4
[1] done
[email] Receive message：this is user registe message5
[1] done
[email] Receive message：this is user registe message6
[1] done
[email] Receive message：this is user registe message7
[1] done
[email] Receive message：this is user registe message8
[1] done
[email] Receive message：this is user registe message9
[1] done

4、消费者2（ReceivePhone）

public class ReceivePhone
{
    //交换机名称
    private final static String EXCHANGE_NAME = "test_exchange_fanout";
    
    //队列名称
    private static final String QUEUE_NAME    = "test_queue_phone";
    
    public static void main(String[] args)
    {
        try
        {
            
            //获取连接
            Connection connection = ConnectionUtil.getConnection();
            //从连接中获取一个通道
            final Channel channel = connection.createChannel();
            //声明交换机（分发:发布/订阅模式）
            channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
            //声明队列
            channel.queueDeclare(QUEUE_NAME, false, false, false, null);
            //将队列绑定到交换机
            channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "");
            //保证一次只分发一个  
            int prefetchCount = 1;
            channel.basicQos(prefetchCount);
            //定义消费者
            DefaultConsumer consumer = new DefaultConsumer(channel)
            {
                //当消息到达时执行回调方法
                @Override
                public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties,
                        byte[] body) throws IOException
                {
                    String message = new String(body, "utf-8");
                    System.out.println("[phone] Receive message：" + message);
                    try
                    {
                        //消费者休息2s处理业务
                        Thread.sleep(1000);
                    }
                    catch (InterruptedException e)
                    {
                        e.printStackTrace();
                    }
                    finally
                    {
                        System.out.println("[2] done");
                        //手动应答
                        channel.basicAck(envelope.getDeliveryTag(), false);
                    }
                }
            };
            //设置手动应答
            boolean autoAck = false;
            //监听队列
            channel.basicConsume(QUEUE_NAME, autoAck, consumer);
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    
}

运行结果：
[phone] Receive message：this is user registe message0
[2] done
[phone] Receive message：this is user registe message1
[2] done
[phone] Receive message：this is user registe message2
[2] done
[phone] Receive message：this is user registe message3
[2] done
[phone] Receive message：this is user registe message4
[2] done
[phone] Receive message：this is user registe message5
[2] done
[phone] Receive message：this is user registe message6
[2] done
[phone] Receive message：this is user registe message7
[2] done
[phone] Receive message：this is user registe message8
[2] done
[phone] Receive message：this is user registe message9
[2] done

总结：

　　1、该模式下生产者并不是直接操作队列，而是将数据发送给交换机，由交换机将数据发送给与之绑定的队列。从运行结果中可以看到，两中类型的消费者（Email，Phone）都收到相同数量的消息。

　　2、该模式必须声明交换机，并且设置模式：channel.exchangeDeclare(EXCHANGE_NAME, "fanout")　　fanout指分发模式（将每一条消息都发送到与交换机绑定的队列。

　　3、 队列必须绑定交换机：channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "");

注意：本文仅代表个人理解和看法哟！和本人所在公司和团体无任何关系！