rabbimq之死信队列

死信队列:DLX，dead-letter-exchange

利用dlx，当消息在一个队列中变成死信(dead message)之后，它能被重新publish到另一个exchange，这个exchange就是dlx

消息变成死信的原因有:

1.消息被拒绝(basic.reject / basic.nack)并且reQueue=false

2.消息TTL过期

3.队列达到最大长度了

1.声明死信队列，交换机等。

import org.springframework.amqp.core.*;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;
import java.util.Map;

@Configuration
public class RabbitMQConfig {

    //死信队里s

    @Bean("deadLetterExchange")
    public Exchange deadLetterExchange() {
        return ExchangeBuilder.directExchange("DL_EXCHANGE").durable(true).build();
    }


    @Bean("deadLetterQueue")
    public Queue deadLetterQueue() {
        Map<String, Object> args = new HashMap<>(2);
        //       x-dead-letter-exchange    声明  死信交换机
        args.put("x-dead-letter-exchange", "DL_EXCHANGE");
        //       x-dead-letter-routing-key    声明 死信路由键
        args.put("x-dead-letter-routing-key", "KEY_R");
        return QueueBuilder.durable("DL_QUEUE").withArguments(args).build();
    }

    @Bean("redirectQueue")
    public Queue redirectQueue() {
        return QueueBuilder.durable("REDIRECT_QUEUE").build();
    }

    /**
     * 死信路由通过 DL_KEY 绑定键绑定到死信队列上.
     *
     * @return the binding
     */
    @Bean
    public Binding deadLetterBinding() {
        return new Binding("DL_QUEUE", Binding.DestinationType.QUEUE, "DL_EXCHANGE", "DL_KEY", null);

    }


    /**
     * 死信路由通过 KEY_R 绑定键绑定到死信队列上.
     *
     * @return the binding
     */
    @Bean
    public Binding redirectBinding() {
        return new Binding("REDIRECT_QUEUE", Binding.DestinationType.QUEUE, "DL_EXCHANGE", "KEY_R", null);
    }


    //死信队里e
}

当DL_KEY 对应的队列中存在死信时，rabbitMQ就会自动的将这个消息重新发布到设置的exchange上去，进而被路由到KEY_R对应的队列。

。

2.生产者：

import org.springframework.amqp.core.MessagePostProcessor;
import org.springframework.amqp.core.MessageProperties;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.amqp.rabbit.support.CorrelationData;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.util.UUID;

/**
 * Created by Jim on 2018/11/24.
 */
@Component
public class DLQueue {

    @Autowired
    private RabbitTemplate rabbitTemplate;

    public void sendMsg(String content) {
        CorrelationData correlationId = new CorrelationData(UUID.randomUUID().toString());
        MessagePostProcessor messagePostProcessor = message -> {
            MessageProperties messageProperties = message.getMessageProperties();
            //            设置编码
            messageProperties.setContentEncoding("utf-8");
            //            设置过期时间10*1000毫秒
            messageProperties.setExpiration("5000");
            return message;
        };
        rabbitTemplate.convertAndSend("DL_EXCHANGE", "DL_KEY", content, messagePostProcessor);
    }
}

这里设置了5000的过期时间，一旦消息到了过期时间还没被正常消费，就会变成死信。

3.DL_KEY 对应的消费者：

@Component
public class DlxMessageReceiver1 {
    @RabbitHandler
    @RabbitListener(queues = "DL_QUEUE")//方法级注解
    public void process(String msg, Channel channel, Message message){
        System.out.println("死信DL_KEY收到  : " + msg );
        System.out.println(1/0);
       
    }

}
     

为了测试，这里注意不要捕获异常，捕获了异常的话，不会进入死信。

4.KEY_R对应的消费者

@Component
public class DlxMessageReceiver {
    @RabbitHandler
    @RabbitListener(queues = "REDIRECT_QUEUE")
    public void process(String msg, Channel channel, Message message)throws Exception {
        System.out.println("死信KEY_R: " +msg);
        channel.basicAck(message.getMessageProperties().getDeliveryTag(),false);
    }
}

在上面2中我们设置了5秒的过期时间，下面我们看看是不是5秒过后就变成死信。

第一次消费失败的时间是：2018-11-24 20:57:11.949 

死信DL_KEY  : 123
2018-11-24 20:57:11.949  WARN 616 --- [cTaskExecutor-1] s.a.r.l.ConditionalRejectingErrorHandler : Execution of Rabbit message listener failed.

最后一次消费失败的时间是：2018-11-24 20:57:13.871

死信DL_KEY : 123
2018-11-24 20:57:13.871 WARN 616 --- [cTaskExecutor-1] s.a.r.l.ConditionalRejectingErrorHandler : Execution of Rabbit message listener failed.
死信KEY_R: 123

由结果来看，好像没到5秒就过期了，我也不是很明白，有空再研究。