《RabbitMQ》什么是死信队列

public class DirectConsumer {
    @RabbitListener(bindings = {
            @QueueBinding(value = @Queue(value = "javatrip",arguments = 
                    {@Argument(name="x-dead-letter-exchange",value = "deadExchange"),
                     @Argument(name="x-dead-letter-routing-key",value = "deadKey")
                    }),
                    exchange = @Exchange(value="javatripDirect"),
                    key = {"info","error","warning"}
            )
    })
public void receive1(String message, @Headers Map<String,Object> headers, Channel channel)throws Exception{
    System.out.println("消费者1"+message);
}

public void publishMessage(String message){

    rabbitTemplate.setMandatory(true);
    rabbitTemplate.convertAndSend("javatripDirect","info",message);
}

spring:
  rabbitmq:
    listener:
      simple:
        acknowledge-mode: manual

Long deliverTag = (Long) headers.get(AmqpHeaders.DELIVERY_TAG);
channel.basicNack(deliverTag,false,false);

@RabbitListener(bindings = {
    @QueueBinding(
        value = @Queue(value = "javatripDead"),
        exchange = @Exchange(value = "deadExchange"),
        key = "deadKey"
    )
})
public void receive2(String message){
    System.out.println("我是一条死信:"+message);
}

@RabbitListener(bindings = {
            @QueueBinding(value = @Queue(value = "javatrip",arguments =
                    {@Argument(name="x-dead-letter-exchange",value = "deadExchange"),
                     @Argument(name="x-dead-letter-routing-key",value = "deadKey"),
                     @Argument(name = "x-message-ttl",value = "3000")
                    }),
                    exchange = @Exchange(value="javatripDirect"),
                    key = {"info","error","warning"}
            )
    })
public void receive1(String message, @Headers Map<String,Object> headers, Channel channel)throws Exception{
    System.out.println("消费者1"+message);
}

@RabbitListener(bindings = {
            @QueueBinding(value = @Queue(value = "javatrip",arguments =
                    {@Argument(name="x-dead-letter-exchange",value = "deadExchange"),
                     @Argument(name="x-dead-letter-routing-key",value = "deadKey"),
                     @Argument(name = "x-max-length",value = "3")
                    }),
                    exchange = @Exchange(value="javatripDirect"),
                    key = {"info","error","warning"}
            )
    })
public void receive1(String message, @Headers Map<String,Object> headers, Channel channel)throws Exception{
    System.out.println("消费者1"+message);
}

@Target({})
@Retention(RetentionPolicy.RUNTIME)
public @interface QueueBinding {

    /**
     * @return the queue.
     */
    Queue value();

    /**
     * @return the exchange.
     */
    Exchange exchange();

    /**
     * @return the routing key or pattern for the binding.
     * Multiple elements will result in multiple bindings.
     */
    String[] key() default {};
}

@Target({})
@Retention(RetentionPolicy.RUNTIME)
public @interface Queue {

    /**
     * @return the queue name or "" for a generated queue name (default).
     */
    @AliasFor("name")
    String value() default "";

    /**
     * @return the queue name or "" for a generated queue name (default).
     * @since 2.0
     */
    @AliasFor("value")
    String name() default "";

    /**
     * 是否持久化
     */
    String durable() default "";

    /**
     * 是否独享、排外的.
     */
    String exclusive() default "";

    /**
     * 是否自动删除；
     */
    String autoDelete() default "";

    /**
     * 队列的其他属性参数
     * （1）x-message-ttl：消息的过期时间，单位：毫秒；
     *（2）x-expires：队列过期时间，队列在多长时间未被访问将被删除，单位：毫秒；
     *（3）x-max-length：队列最大长度，超过该最大值，则将从队列头部开始删除消息；
     *（4）x-max-length-bytes：队列消息内容占用最大空间，受限于内存大小，超过该阈值则从队列头部开始删除消      * 息；
     *（5）x-overflow：设置队列溢出行为。这决定了当达到队列的最大长度时消息会发生什么。有效值是drop-         * head、reject-publish或reject-publish-dlx。仲裁队列类型仅支持drop-head；
     *（6）x-dead-letter-exchange：死信交换器名称，过期或被删除（因队列长度超长或因空间超出阈值）的消息       * 可指定发送到该交换器中；
     *（7）x-dead-letter-routing-key：死信消息路由键，在消息发送到死信交换器时会使用该路由键，如果不设         * 置，则使用消息的原来的路由键值
     *（8）x-single-active-consumer：表示队列是否是单一活动消费者，true时，注册的消费组内只有一个消费     * 者消费消息，其他被忽略，false时消息循环分发给所有消费者(默认false)
     *（9）x-max-priority：队列要支持的最大优先级数;如果未设置，队列将不支持消息优先级；
     *（10）x-queue-mode（Lazy mode）：将队列设置为延迟模式，在磁盘上保留尽可能多的消息，以减少RAM的使         * 用;如果未设置，队列将保留内存缓存以尽可能快地传递消息；
     *（11）x-queue-master-locator：在集群模式下设置镜像队列的主节点信息。
     */
    Argument[] arguments() default {};
}

@Target({})
@Retention(RetentionPolicy.RUNTIME)
public @interface Exchange {

    String TRUE = "true";

    String FALSE = "false";

    /**
     * @return the exchange name.
     */
    @AliasFor("name")
    String value() default "";

    /**
     * @return the exchange name.
     * @since 2.0
     */
    @AliasFor("value")
    String name() default "";

    /**
     * 交换机类型，默认DIRECT
     */
    String type() default ExchangeTypes.DIRECT;

    /**
     * 是否持久化
     */
    String durable() default TRUE;

    /**
     * 是否自动删除
     */
    String autoDelete() default FALSE;

    /**
     * @return the arguments to apply when declaring this exchange.
     * @since 1.6
     */
    Argument[] arguments() default {};
}