消息中间件Rabbit(七)-死信队列

旧城等待， 2023-10-06 21:09 16阅读 0赞

## 一、死信队列的概念 ##

死信队列：无法被消费的消息

应用场景:为了保证订单业务的消息数据不丢失，需要使用到 RabbitMQ 的死信队列机制，当消息 消费发生异常时，将消息投入死信队列中.还有比如说: 用户在商城下单成功并点击去支付后在指定时间未支付时自动失效

## 二、死信的来源 ##

1. 消息TTL过期

2.队列达到最大长度(队列满了，无法再添加数据到mq中)

3.消息被拒绝(basic.reject或basic.nack)并且requeue=false。

## 三、死信代码实现 ##

### 3.1 代码架构图 ###

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA6Iqx5p6c5rC06I6y_size_20_color_FFFFFF_t_70_g_se_x_16][]

### 3.2 消息TTL过期 ###

**生产者代码**

public class Producer {
        private final static  String NORMAL_EXCHANGE="normal_exchange";
        public static void main(String[] args) throws IOException, TimeoutException, InterruptedException {
            //获取链接对象
            Connection connection= RabbitMqUtils.getConnection();
            Channel channel = connection.createChannel();
    
            channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
            //设置消息的TTL时间
            AMQP.BasicProperties properties=new AMQP.BasicProperties().builder().expiration("10000").build();
            for(int i=1;i<11;i++)
            {
                String message="info"+i;
              channel.basicPublish(NORMAL_EXCHANGE,"zhangsan",properties,message.getBytes());
            }
        }
    }

**消费者C1代码（启动之后关闭该消费者 模拟其接收不到消息）**

public class Concumer01 {
        private final static  String NORMAL_EXCHANGE="normal_exchange";
        private final static  String DEAD_EXCHANGE="dead_exchange";
        public static void main(String[] args) throws IOException, TimeoutException {
            Connection connection=RabbitMqUtils.getConnection();
            Channel channel = connection.createChannel();
            //声明两个交换机
            channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
            channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
    
            //声明死信队列
            String dead_queue = "dead_queue";
            channel.queueDeclare(dead_queue,false,false,false,null);
            channel.queueBind(dead_queue,DEAD_EXCHANGE,"lisi");
    
            //声明普通队列
            String normal_queue = "normal_queue";
            //正常队列绑定死信队列
            Map<String,Object> params = new HashMap<>();
            //正常队列设置死信交换机，参数key是固定值
            params.put("x-dead-letter-exchange",DEAD_EXCHANGE);
            //正常队列设置死信routing-key 参数key是固定值
            params.put("x-dead-letter-routing-key","lisi");
            channel.queueDeclare(normal_queue,false,false,false,params);
            channel.queueBind(normal_queue,NORMAL_EXCHANGE,"zhangsan");
    
            System.out.println("等待接收消息......");
    
    
            //推送的消息如何进行消费的接口回调
            DeliverCallback deliverCallback = (consumerTag,delivery)->{
                String message = new String(delivery.getBody(),"UTF-8");
                System.out.println("Concumer01收到的信息"+message);
            };
    
                CancelCallback cancelCallback = (consumerTag)->{
                  System.out.println("消息消费被中断");
                };
    
                boolean autoAck = true;
                channel.basicConsume(normal_queue,autoAck,deliverCallback,cancelCallback);
    
        }
    }

### 3.3 队列达到最大长度 ###

1. 生产者去掉TTL属性

public class Producer {
    
        private final static  String NORMAL_EXCHANGE="normal_exchange";
        public static void main(String[] args) throws IOException, TimeoutException, InterruptedException {
            //获取链接对象
            Connection connection= RabbitMqUtils.getConnection();
            Channel channel = connection.createChannel();
    
            channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
            for(int i=1;i<11;i++)
            {
                String message="info"+i;
                channel.basicPublish(NORMAL_EXCHANGE,"zhangsan",null,message.getBytes());
            }
        }
    }

2. C1消费者添加设置正常队列长度的限制

params.put("x-max-length",6);

public class Concumer01 {
        private final static  String NORMAL_EXCHANGE="normal_exchange";
        private final static  String DEAD_EXCHANGE="dead_exchange";
        public static void main(String[] args) throws IOException, TimeoutException {
            Connection connection=RabbitMqUtils.getConnection();
            Channel channel = connection.createChannel();
            //声明两个交换机
            channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
            channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
    
            //声明死信队列
            String dead_queue = "dead_queue";
            channel.queueDeclare(dead_queue,false,false,false,null);
            channel.queueBind(dead_queue,DEAD_EXCHANGE,"lisi");
    
            //声明普通队列
            String normal_queue = "normal_queue";
            //正常队列绑定死信队列
            Map<String,Object> params = new HashMap<>();
            //正常队列设置死信交换机，参数key是固定值
            params.put("x-dead-letter-exchange",DEAD_EXCHANGE);
            //正常队列设置死信routing-key 参数key是固定值
            params.put("x-dead-letter-routing-key","lisi");
            params.put("x-max-length",6);
            channel.queueDeclare(normal_queue,false,false,false,params);
            channel.queueBind(normal_queue,NORMAL_EXCHANGE,"zhangsan");
    
            System.out.println("等待接收消息......");
            //推送的消息如何进行消费的接口回调
            DeliverCallback deliverCallback = (consumerTag,delivery)->{
                String message = new String(delivery.getBody(),"UTF-8");
                System.out.println("Concumer01收到的信息"+message);
            };
                CancelCallback cancelCallback = (consumerTag)->{
                  System.out.println("消息消费被中断");
                };
                boolean autoAck = true;
                channel.basicConsume(normal_queue,autoAck,deliverCallback,cancelCallback);
        }
    }

3. C2消费者代码不变

### 3.4 消息被拒 ###

1.消息生产者代码同上生产者一致

2. C1 消费者代码

public class Consumer01 {
        //普通交换机名称
        private static final String NORMAL_EXCHANGE = "normal_exchange";
        //死信交换机名称
        private static final String DEAD_EXCHANGE = "dead_exchange";
        public static void main(String[] argv) throws Exception {
            Connection connection= RabbitMqUtils.getConnection();
            Channel channel = connection.createChannel();
            //声明死信和普通交换机 类型为 direct
            channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
            channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
            //声明死信队列
            String deadQueue = "dead-queue";
            channel.queueDeclare(deadQueue, false, false, false, null);
            //死信队列绑定死信交换机与 routingkey
            channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
            
            //正常队列绑定死信队列信息
            Map<String, Object> params = new HashMap<>();
            //正常队列设置死信交换机 参数 key 是固定值
            params.put("x-dead-letter-exchange", DEAD_EXCHANGE);
            //正常队列设置死信 routing-key 参数 key 是固定值
            params.put("x-dead-letter-routing-key", "lisi");
            String normalQueue = "normal-queue";
            channel.queueDeclare(normalQueue, false, false, false, params);
            channel.queueBind(normalQueue, NORMAL_EXCHANGE, "zhangsan");
            System.out.println("等待接收消息........... ");
            DeliverCallback deliverCallback = (consumerTag, delivery) ->{
                String message = new String(delivery.getBody(), "UTF-8");
                if(message.equals("info5")){
                    System.out.println("Consumer01 接收到消息" + message + "并拒绝签收该消息");
                    //requeue 设置为 false 代表拒绝重新入队 该队列如果配置了死信交换机将发送到死信队列中
                    channel.basicReject(delivery.getEnvelope().getDeliveryTag(), false);
                }else {
                    System.out.println("Consumer01 接收到消息"+message);
                    channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
                }
            };
            boolean autoAck = false;
            channel.basicConsume(normalQueue, autoAck, deliverCallback, consumerTag -> {});
        }
    }

注意：代码中要实现拒绝消息，autoAck必须设置成false，即手动应答。

3. C2消费者代码同上消费者一致。

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