RabbitMQ之死信队列

1.死信

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

2.发生死信的情形

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

3.示例

情景①：Time to live 过期

生产者相关代码

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 <= 10 ; 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相关代码，执行完关闭C1，模拟接收不到消息超时

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 = 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 -> {});
    }
}

消费者C2相关代码，接收超时10s的消息，由C2消费

public class Consumer02 {
    private static final String DEAD_EXCHANGE = "dead_exchange";
    public static void main(String[] argv) throws Exception {
        Channel channel = RabbitMqUtils.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 -> {});
    }
}

情景②：队列达到最大长度

1.生产者注释TTL相关代码

2.消费者C1增加如下代码

//设置正常队列长度的限制
params.put("x-max-length", 6);
//注意此时需要把原先队列删除 因为参数改变了

3.消费者C2不变

情景③：消息被拒收

生产者和消费者C2不变

修改消费者C1代码如下：

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 -> {});

4.小结