04-死信队列 | banner の blog

# 一、什么是死信队列

当一条消息在队列中出现以下三种情况的时候，该消息就会变成一条死信。

消息被拒绝(basic.reject / basic.nack)，并且requeue = false
消息TTL过期
队列达到最大长度

当消息在一个队列中变成一个死信之后，如果配置了死信队列，它将被重新publish到死信交换机，死信交换机将死信投递到一个队列上，这个队列就是死信队列。

# 二、实现死信队列

# 2.1 原理

# 2.2 消息过期成为死信

消费者01，创建队列，并设置普通队列参数指定死信的交换机和死信RoutingKey。

public class Consumer01 {
    //普通交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    //死信交换机
    public static final String DEAD_EXCHANGE = "dead_exchange";
    //普通队列名称
    public static final String NORMAL_QUEUE = "normal_queue";
    //死信队列名称
    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
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//设置死信交换机
        arguments.put("x-dead-letter-routing-key", "lisi");//设置死信RoutingKey
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);

        //队列绑定交换机
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhansan");
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");

        System.out.println("等待接收消息...");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer01接收消息：" + new String(message.getBody(), StandardCharsets.UTF_8));

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

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关闭消费者1，生产者发送10s过期的消息给普通交换机。

public class Producer {
    //普通交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";

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

        AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();

        //死信消息
        for (int i = 1; i < 11; i++) {
            String message = "info：" + i;
            channel.basicPublish(NORMAL_EXCHANGE, "zhansan", properties, message.getBytes(StandardCharsets.UTF_8));
        }
    }
}

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没有消费的消息，被转发给死信交换机，发送到死信队列，被消费者2消费

public class Consumer02 {
    //死信队列名称
    public static final String DEAD_QUEUE = "dead_queue";

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

        System.out.println("等待接收消息...");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer02 接收消息：" + new String(message.getBody(), StandardCharsets.UTF_8));

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

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# 2.2 队列达到最大长度

设置队列的最大长度，超出部分成为死信

arguments.put("x-max-length", 6);//设置队列长度限制,超出部分为死信

public class Consumer01 {
    //普通交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    //死信交换机
    public static final String DEAD_EXCHANGE = "dead_exchange";
    //普通队列名称
    public static final String NORMAL_QUEUE = "normal_queue";
    //死信队列名称
    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
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//设置死信交换机
        arguments.put("x-dead-letter-routing-key", "lisi");//设置死信RoutingKey
        arguments.put("x-max-length", 6);//设置队列长度限制,超出部分为死信
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);

        //队列绑定交换机
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhansan");
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");

        System.out.println("等待接收消息...");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            System.out.println("Consumer01接收消息：" + new String(message.getBody(), StandardCharsets.UTF_8));

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

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# 2.3 消息被拒绝成为死信

修改消费者01，去除队列最大长度限制，修改为手动应答，将某一条消息应答设置为拒绝并 不放回队列 成为死信消息

public class Consumer01 {
    //普通交换机
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    //死信交换机
    public static final String DEAD_EXCHANGE = "dead_exchange";
    //普通队列名称
    public static final String NORMAL_QUEUE = "normal_queue";
    //死信队列名称
    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
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);

        //声明普通队列
        HashMap<String, Object> arguments = new HashMap<>();
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);//设置死信交换机
        arguments.put("x-dead-letter-routing-key", "lisi");//设置死信RoutingKey
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);

        //队列绑定交换机
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhansan");
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");

        System.out.println("等待接收消息...");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
            String msg = new String(message.getBody(), StandardCharsets.UTF_8);
            if (msg.equals("info：5")) {
                channel.basicReject(message.getEnvelope().getDeliveryTag(), false);
            } else {
                System.out.println("Consumer01接收消息：" + msg);
                channel.basicAck(message.getEnvelope().getDeliveryTag(), false);
            }
        };
        channel.basicConsume(NORMAL_QUEUE, false, deliverCallback, consumerTag -> {
        });
    }
}

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