RabbitMQ - 7. 死信 - 《java学习》

7.1 死信的概念
7.2 死信的来源
7.3 死信实战

7.1 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

7.2 死信的来源

消息 TTL 过期

TTL是Time To Live的缩写, 也就是生存时间

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.

7.3 死信实战

1、死信之TTl

生产者：

package com.hao.rabbitmq.eight;
import com.hao.rabbitmq.utils.RabbitMqUtils;
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
/**
 * @author shkstart
 * @create 2021-09 15:13
 *
 * 死信队列 生产者代码
 */
public class Producer {
    //普通交换机的名称
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        //死信消息 设置TTL时间 time to live 单位是ms
        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：

package com.hao.rabbitmq.eight;
import com.hao.rabbitmq.utils.RabbitMqUtils;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DeliverCallback;
import java.util.HashMap;
/**
 * @author shkstart
 * @create 2021-09 16:37
 *
 *  死信队列 实战
 *  消费者1
 *
 */
public class Consumer01 {
    //普通交换机的名称
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    //死信交换机的名称
    public static final String DEAD_EXCHANGE = "dead_exchange";
    //普通队列的名称
    public static final String NORMAL_QUEUE = "normal_queue";
    //私信队列的名称
    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 类型为direct
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
        HashMap<String, Object> arguments = new HashMap<>();
        //过期时间 10s=10000ms
        //arguments.put("x-message-ttl", 10000);
        //正常队列设置死信交换机
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);
        //设置死信RoutionKey
        arguments.put("x-dead-letter-routing-key", "lisi");
        //声明普通队列
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
        //绑定普通交换机与队列
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhangsan");
        //绑定死信的交换机与死信的队列
        channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "lisi");
        System.out.println("等待接收消息......");
        DeliverCallback deliverCallback = (consumerTag, message) ->{
            System.out.println("Consumer01接收的消息是：" + new String(message.getBody(),"UTF-8"));
        };
        channel.basicConsume(NORMAL_QUEUE, true, deliverCallback, consumerTag ->{});
    }
}

消费者C2（处理死信）：

package com.hao.rabbitmq.eight;
import com.hao.rabbitmq.utils.RabbitMqUtils;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DeliverCallback;
import java.util.HashMap;
/**
 * @author shkstart
 * @create 2021-09 16:37
 *
 *  死信队列 实战
 *  消费者1
 *
 */
public class Consumer02 {
    //私信队列的名称
    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接收的消息是：" + new String(message.getBody(),"UTF-8"));
        };
        channel.basicConsume(DEAD_QUEUE, true, deliverCallback, consumerTag ->{});
    }
}

启动 C1 ，之后关闭消费者，模拟其接收不到消息。再启动 Producer

启动 C2 消费者，它消费死信队列里面的消息

2、死信之最大长度

①消息生产者代码去掉 TTL 属性

②C1 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)

//设置正常队列的长度限制，例如发10个，4个则为死信
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、消息被拒绝

①消息生产者代码同上生产者一致
②C1 消费者代码(启动之后关闭该消费者模拟其接收不到消息)

拒收消息 “info5”

package com.hao.rabbitmq.eight;
import com.hao.rabbitmq.utils.RabbitMqUtils;
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
/**
 * @author shkstart
 * @create 2021-09 15:13
 *
 * 死信队列 生产者代码
 */
public class Producer {
    //普通交换机的名称
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMqUtils.getChannel();
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        //死信消息 设置TTL时间 time to live 单位是ms
        //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", null, message.getBytes());
        }
    }
}

package com.hao.rabbitmq.eight;
import com.hao.rabbitmq.utils.RabbitMqUtils;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DeliverCallback;
import java.util.HashMap;
/**
 * @author shkstart
 * @create 2021-09 16:37
 *
 *  死信队列 实战
 *  消费者1
 *
 */
public class Consumer01 {
    //普通交换机的名称
    public static final String NORMAL_EXCHANGE = "normal_exchange";
    //死信交换机的名称
    public static final String DEAD_EXCHANGE = "dead_exchange";
    //普通队列的名称
    public static final String NORMAL_QUEUE = "normal_queue";
    //私信队列的名称
    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 类型为direct
        channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
        HashMap<String, Object> arguments = new HashMap<>();
        //过期时间 10s=10000ms
        //arguments.put("x-message-ttl", 10000);
        //正常队列设置死信交换机
        arguments.put("x-dead-letter-exchange", DEAD_EXCHANGE);
        //设置死信RoutionKey
        arguments.put("x-dead-letter-routing-key", "lisi");
        //设置正常队列的长度的限制，超过的部分成为死信，未超过的部分正常接收
        //arguments.put("x-max-length", 6);
        //声明普通队列
        channel.queueDeclare(NORMAL_QUEUE, false, false, false, arguments);
        //声明死信队列
        channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
        //绑定普通交换机与队列
        channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "zhangsan");
        //绑定死信的交换机与死信的队列
        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(), "UTF-8");
            if(msg.equals("info5")){
                System.out.println("拒绝消息：" + msg);
                channel.basicReject(message.getEnvelope().getDeliveryTag(), false);
            }else{
                System.out.println("Consumer01接收的消息是：" + msg);
                channel.basicAck(message.getEnvelope().getDeliveryTag(), false);
            }
        };
        //开启手动应答
        channel.basicConsume(NORMAL_QUEUE, false, deliverCallback, consumerTag ->{});
    }
}

③C2 消费者代码不变
启动消费者 1 然后再启动消费者 2