SpringBoot：RabbitMQ-延迟队列，通过五轮面试斩获offer阿里实习生亲述

RabbitMQ 实现思路

RabbitMQ队列本身是没有直接实现支持延迟队列的功能，但可以通过它的Time-To-Live Extensions 与 Dead Letter Exchange 的特性模拟出延迟队列的功能。

Time-To-Live Extensions

RabbitMQ支持为队列或者消息设置TTL（time to live 存活时间）。TTL表明了一条消息可在队列中存活的最大时间。当某条消息被设置了TTL或者当某条消息进入了设置了TTL的队列时，这条消息会在TTL时间后死亡成为Dead Letter。如果既配置了消息的TTL，又配置了队列的TTL，那么较小的那个值会被取用。

Dead Letter Exchange

死信交换机，上文中提到设置了 TTL 的消息或队列最终会成为Dead Letter。如果为队列设置了Dead Letter Exchange（DLX），那么这些Dead Letter就会被重新发送到Dead Letter Exchange中，然后通过Dead Letter Exchange路由到其他队列，即可实现延迟队列的功能。

导入依赖

在 pom.xml 中添加 spring-boot-starter-amqp的依赖

org.springframework.boot spring-boot-starter-amqp com.alibaba fastjson 1.2.46 org.springframework.boot spring-boot-starter-web org.springframework.boot spring-boot-starter-test test 属性配置

在 application.properties 文件中配置rabbitmq相关内容，值得注意的是这里配置了手动ACK的开关

spring.rabbitmq.username=battcn
spring.rabbitmq.password=battcn
spring.rabbitmq.host=192.168.0.133
spring.rabbitmq.port=5672
spring.rabbitmq.virtual-host=/

手动ACK 不开启自动ACK模式,目的是防止报错后未正确处理消息丢失 默认 为 none

spring.rabbitmq.listener.simple.acknowledge-mode=manual

具体编码 定义队列

如果手动创建过或者RabbitMQ中已经存在该队列那么也可以省略下述代码…

package com.battcn.config;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.amqp.core.*;
import org.springframework.amqp.rabbit.connection.CachingConnectionFactory;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

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

@Configuration
public class RabbitConfig {

private static final Logger log = LoggerFactory.getLogger(RabbitConfig.class);

@Bean
public RabbitTemplate rabbitTemplate(CachingConnectionFactory connectionFactory) {
connectionFactory.setPublisherConfirms(true);
connectionFactory.setPublisherReturns(true);
RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
rabbitTemplate.setMandatory(true);
rabbitTemplate.setConfirmCallback((correlationData, ack, cause) -> log.info(“消息发送成功:correlationData({}),ack({}),cause({})”, correlationData, ack, cause));
rabbitTemplate.setReturnCallback((message, replyCode, replyText, exchange, routingKey) -> log.info(“消息丢失:exchange({}),route({}),replyCode({}),replyText({}),message:{}”, exchange, routingKey, replyCode, replyText, message));
return rabbitTemplate;
}

public static final String DELAY_ROUTING_KEY = “”;

public static final String REGISTER_QUEUE_NAME = “dev.book.register.queue”;
public static final String REGISTER_EXCHANGE_NAME = “dev.book.register.exchange”;
public static final String ROUTING_KEY = “all”;

@Bean
public Queue delayProcessQueue() {
Map params = new HashMap<>();
// x-dead-letter-exchange 声明了队列里的死信转发到的DLX名称，
params.put(“x-dead-letter-exchange”, REGISTER_EXCHANGE_NAME);
// x-dead-letter-routing-key 声明了这些死信在转发时携带的 routing-key 名称。
params.put(“x-dead-letter-routing-key”, ROUTING_KEY);
return new Queue(REGISTER_DELAY_QUEUE, true, false, false, params);
}

@Bean
public DirectExchange delayExchange() {
return new DirectExchange(REGISTER_DELAY_EXCHANGE);
}

@Bean
public Binding dlxBinding() {
return BindingBuilder.bind(delayProcessQueue()).to(delayExchange()).with(DELAY_ROUTING_KEY);
}

@Bean
public Queue registerBookQueue() {
return new Queue(REGISTER_QUEUE_NAME, true);
}

@Bean
public TopicExchange registerBookTopicExchange() {
return new TopicExchange(REGISTER_EXCHANGE_NAME);
}

@Bean
public Binding registerBookBinding() {
// TODO 如果要让延迟队列之间有关联,这里的 routingKey 和 绑定的交换机很关键
return BindingBuilder.bind(registerBookQueue()).to(registerBookTopicExchange()).with(ROUTING_KEY);
}

}

实体类

创建一个Book类

public class Book implements java.io.Serializable {

private static final long serialVersionUID = -2164058270260403154L;

private String id;
private String name;
// 省略get set …
}

控制器

编写一个Controller类，用于消息发送工作，同时为了看到测试效果，添加日志输出，将发送消息的时间记录下来…

package com.battcn.controller;

import com.battcn.config.RabbitConfig;
import com.battcn.entity.Book;
import com.battcn.handler.BookHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.amqp.support.converter.AbstractJavaTypeMapper;
import org.springframework.beans.factory.annotation.Autowir

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ed;
import org.springframework.web.bind.annotation.*;

import java.time.LocalDateTime;

@RestController
@RequestMapping(value = “/books”)
public class BookController {

private static final Logger log = LoggerFactory.getLogger(BookController.class);

private final RabbitTemplate rabbitTemplate;

@Autowired
public BookController(RabbitTemplate rabbitTemplate) {
this.rabbitTemplate = rabbitTemplate;
}

@GetMapping
public void defaultMessage() {
Book book = new Book();
book.setId(“1”);
book.setName(“一起来学Spring Boot”);
fig.REGISTER_DELAY_EXCHANGE, RabbitConfig.DELAY_ROUTING_KEY, book); 对应 {@link BookHandler#listenerDelayQueue}
*/
@GetMapping
public void defaultMessage() {
Book book = new Book();
book.setId(“1”);
book.setName(“一起来学Spring Boot”);