2024-01-14  阅读(58)
原文作者:Java充电社 原文地址: http://www.itsoku.com/course/22/388

10.1、死信的概念

先从概念解释上搞清楚这个定义,死信,顾名思义就是无法被消费的消息,字面意思可以这样理解,一般来说, producer 将消息投递到 broker 或者直接到 queue 里了, consumer 从 queue 取出消息进行消费,但某些时候由于特定的原因导致 queue 中的某些消息无法被消费,这样的消息如果没有后续的处理,就变成了死信,有死信自然就有了死信队列。

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

10.2、死信的来源(3种)

  • 消息 TTL 过期
  • 队列达到最大长度(队列满了,无法再添加数据到 mq 中)
  • 消息被拒绝(basic.reject 或 basic.nack)并且 requeue=false.

10.3、死信实战

1)代码架构图

202401142236392161.png

2)消息TTL过期(可实现延迟消息)

生产者代码

    public class Producer {
        private static final String NORMAL_EXCHANGE = "normal_exchange";
    
        public static void main(String[] argv) throws Exception {
            try (Channel channel = RabbitMqUtils.getChannel()) {
                channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
                //设置消息的 TTL 时间
                AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();
                //该信息是用作演示队列个数限制
                for (int i = 1; i < 11; i++) {
                    String message = "info" + i;
                    channel.basicPublish(NORMAL_EXCHANGE, "zhangsan", properties, message.getBytes());
                    System.out.println("生产者发送消息:" + message);
                }
            }
        }
    }

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 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 {
            Channel channel = RabbitUtils.getChannel();
            //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");
                System.out.println("Consumer01 接收到消息"+message);
            };
            channel.basicConsume(normalQueue, true, deliverCallback, consumerTag -> {
            });
        }
    }

202401142236396582.png

消费者 C2 代码(以上步骤完成后 启动 C2 消费者 它消费死信队列里面的消息)

    public class Consumer02 {
        private static final String DEAD_EXCHANGE = "dead_exchange";
    
        public static void main(String[] argv) throws Exception {
            Channel channel = RabbitUtils.getChannel();
            channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
            String deadQueue = "dead-queue";
            channel.queueDeclare(deadQueue, false, false, false, null);
            channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
            System.out.println("等待接收死信队列消息.....");
            DeliverCallback deliverCallback = (consumerTag, delivery) -> {
                String message = new String(delivery.getBody(), "UTF-8");
                System.out.println("Consumer02 接收死信队列的消息" + message);
            };
            channel.basicConsume(deadQueue, true, deliverCallback, consumerTag -> {
            });
        }
    }

202401142236403973.png

3)队列达到最大长度

消息生产者代码去掉 TTL 属性

    public class Producer {
        private static final String NORMAL_EXCHANGE = "normal_exchange";
        public static void main(String[] argv) throws Exception {
            try (Channel channel = RabbitMqUtils.getChannel()) {
                channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
                //该信息是用作演示队列个数限制
                for (int i = 1; i <11 ; i++) {
                    String message="info"+i;
                    channel.basicPublish(NORMAL_EXCHANGE,"zhangsan",null, message.getBytes());
                    System.out.println("生产者发送消息:"+message);
                }
            }
        }
    }

C1 消费者修改以下代码(启动之后关闭该消费者 模拟其接收不到消息 )

202401142236409834.png

注意此时需要把原先队列删除 因为参数改变了

C2 消费者代码不变(启动 C2 消费者)

202401142236415995.png

4)消息拒绝

  1. 消息生产者代码同上生产者一致
  2. C1 消费者代码(启动之后关闭该消费者 模拟其接收不到消息)
    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 {
            Channel channel = RabbitUtils.getChannel();
            //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 -> {
            });
        }
    }

202401142236421006.png

C2 消费者代码不变,启动消费者 1,然后再启动消费者 2

202401142236426747.png

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