RabbitMQ之死信队列

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。

案例

TLL过期

交换机类型是 direct，两个消费者，一个生产者，两个队列：消息队列和死信队列

/**
 * @author shaoshao
 * @Date 2022/11/23 19:01
 * @Description: 死信队列消费者
 */
public class Consumer01 {
    // 普通和死信交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    public static final String DEAD_EXCHANGE = "dead_exchange";
    // 普通和死信队列
    public static final String NORMAL_QUEUE = "normal_queue";
    public static final String DEAD_QUEUE = "dead_queue";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.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);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        // 过期时间 10s 在生产者那边声明更灵活
        // arguments.put("x-message-ttl", 10000);
        //正常的队列设置死信交换机
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//图中红箭头
        //设置死信routingKey
        arguments.put("x-dead-letter-routing-key", "lisi");
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
        //绑定普通的交换机与队列
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhangSan");
        //绑定死信的交换机与队列
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer01接受的消息是：" + new String(message.getBody(), "UTF-8"));
        };

        channel.basicConsume(NORMAL_QUEUE, true, deliverCallback, consumerTag -> {
        });
    }

}

/**
 * @author shaoshao
 * @Date 2022/11/23 19:01
 * @Description: 死信队列消费者
 */
public class Consumer02 {

    public static final String DEAD_QUEUE = "dead_queue";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();

        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer02接受的消息是：" + new String(message.getBody(), "UTF-8"));
        };

        channel.basicConsume(DEAD_QUEUE, true, deliverCallback, consumerTag -> {
        });
    }

}

/**
 * @author shaoshao
 * @Date 2022/11/23 19:11
 * @Description: 死信队列之生产者
 */
public class Product {
    public static final String NORMAL_EXCHANGE = "normal_exchange";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();
        // 死信队列 设置TTL时间 10s
        AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();

        for (int i = 0; i < 11; i++) {
            String message = "info" + i;
            channel.basicPublish(NORMAL_EXCHANGE, "zhangSan", properties, message.getBytes());
        }
    }
}

先启动C1，然后关闭，模拟C1无法收到消息，然后启动生产者，查看效果。再启动C2接收消息即可

• 未发消息两个队列的状态

• 产者发送了10条消息，此时正常消息队列有10条未消费消息

• 时间过去10秒，正常队列里面的消息由于没有被消费，消息进入死信队列

• 再启动C2（死信队列）接收消息

队列达到最大长度

• 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

/**
 * @author shaoshao
 * @Date 2022/11/23 19:01
 * @Description: 死信队列消费者
 */
public class Consumer01 {
    // 普通和死信交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    public static final String DEAD_EXCHANGE = "dead_exchange";
    // 普通和死信队列
    public static final String NORMAL_QUEUE = "normal_queue";
    public static final String DEAD_QUEUE = "dead_queue";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.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);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        //正常的队列设置死信交换机
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//图中红箭头
        //设置死信routingKey
        arguments.put("x-dead-letter-routing-key", "lisi");
        //设置正常队列的长度限制
        arguments.put("x-max-length", 6);

        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
        //绑定普通的交换机与队列
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhangSan");
        //绑定死信的交换机与队列
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer01接受的消息是：" + new String(message.getBody(), "UTF-8"));
        };

        channel.basicConsume(NORMAL_QUEUE, true, deliverCallback, consumerTag -> {
        });
    }

}

• 消息生产者代码去掉 TTL 属性，basicPublish 的第三个参数改为 null

/**
 * @author shaoshao
 * @Date 2022/11/23 19:11
 * @Description: 死信队列之生产者
 */
public class Product {
    public static final String NORMAL_EXCHANGE = "normal_exchange";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();

        for (int i = 0; i < 11; i++) {
            String message = "info" + i;
            channel.basicPublish(NORMAL_EXCHANGE, "zhangSan", null, message.getBytes());
        }
    }
}

因为参数改变了，所以需要把原先队列删除

• 启动消费者C1，创建出队列，然后停止该 C1 的运行，启动生产者

• 启动C2

• 查看控制台

消息被拒

即可以指定拒绝哪个消息

/**
 * @author shaoshao
 * @Date 2022/11/23 19:01
 * @Description: 死信队列消费者
 */
public class Consumer01 {
    // 普通和死信交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    public static final String DEAD_EXCHANGE = "dead_exchange";
    // 普通和死信队列
    public static final String NORMAL_QUEUE = "normal_queue";
    public static final String DEAD_QUEUE = "dead_queue";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.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);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        //正常的队列设置死信交换机
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//图中红箭头
        //设置死信routingKey
        arguments.put("x-dead-letter-routing-key", "lisi");
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
        //绑定普通的交换机与队列
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhangSan");
        //绑定死信的交换机与队列
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            String msg = new String(message.getBody(),"UTF-8");
            if (msg.equals("info5")){
                System.out.println("Consumer01接收的消息："+msg+" 此消息是被拒绝的");
                channel.basicReject(message.getEnvelope().getDeliveryTag(), false);
            } else {
                System.out.println("Consumer01接收的消息："+msg);
            }

        };
        // 开启手动应答 为消息被拒 false
        channel.basicConsume(NORMAL_QUEUE, false, deliverCallback, consumerTag -> {
        });

    }

}

/**
 * @author shaoshao
 * @Date 2022/11/23 19:01
 * @Description: 死信队列消费者
 */
public class Consumer02 {

    public static final String DEAD_QUEUE = "dead_queue";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();

        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer02接受的消息是：" + new String(message.getBody(), "UTF-8"));
        };

        channel.basicConsume(DEAD_QUEUE, true, deliverCallback, consumerTag -> {
        });
    }

}

/**
 * @author shaoshao
 * @Date 2022/11/23 19:11
 * @Description: 死信队列之生产者
 */
public class Product {
    public static final String NORMAL_EXCHANGE = "normal_exchange";

    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();
        // 死信队列 设置TTL时间 10s
//        AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();

        for (int i = 0; i < 11; i++) {
            String message = "info" + i;
//            channel.basicPublish(NORMAL_EXCHANGE, "zhangSan", properties, message.getBytes());
            channel.basicPublish(NORMAL_EXCHANGE, "zhangSan", null, message.getBytes());
        }
    }
}

• 先启动C1，然后再关闭C1。启动生产者

• 再启动C1消费消息，此时只剩下拒绝的info5消息

• 启动C2