从实现到原理，我总结了11种延迟任务的实现方式（上篇）

@Getter
public class SanYouTask implements Delayed {

    private final String taskContent;

    private final Long triggerTime;

    public SanYouTask(String taskContent, Long delayTime){
        this.taskContent = taskContent;
        this.triggerTime = System.currentTimeMillis() + delayTime * 1000;
    }

    @Override
    public long getDelay(TimeUnit unit){
        return unit.convert(triggerTime - System.currentTimeMillis(), TimeUnit.MILLISECONDS);
    }

    @Override
    public int compareTo(Delayed o){
        return this.triggerTime.compareTo(((SanYouTask) o).triggerTime);
    }

}

@Slf4j
public class DelayQueueDemo {

    public static void main(String[] args){
        DelayQueue<SanYouTask> sanYouTaskDelayQueue = new DelayQueue<>();

        new Thread(() -> {
            while (true) {
                try {
                    SanYouTask sanYouTask = sanYouTaskDelayQueue.take();
                    log.info("获取到延迟任务:{}", sanYouTask.getTaskContent());
                } catch (Exception e) {
                }
            }
        }).start();

        log.info("提交延迟任务");
        sanYouTaskDelayQueue.offer(new SanYouTask("三友的java日记5s", 5L));
        sanYouTaskDelayQueue.offer(new SanYouTask("三友的java日记3s", 3L));
        sanYouTaskDelayQueue.offer(new SanYouTask("三友的java日记8s", 8L));
    }
}

@Slf4j
public class TimerDemo {

    public static void main(String[] args){
        Timer timer = new Timer();

        log.info("提交延迟任务");
        timer.schedule(new TimerTask() {
            @Override
            public void run(){
                log.info("执行延迟任务");
            }
        }, 5000);
    }

}

public abstract class TimerTask implements Runnable {
    //忽略其它属性

    long nextExecutionTime;
}

@Slf4j
public class ScheduledThreadPoolExecutorDemo {

    public static void main(String[] args){
        ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(2, new ThreadPoolExecutor.CallerRunsPolicy());

        log.info("提交延迟任务");
        executor.schedule(() -> log.info("执行延迟任务"), 5, TimeUnit.SECONDS);
    }

}

<dependency>
    <groupId>org.apache.rocketmq</groupId>
    <artifactId>rocketmq-spring-boot-starter</artifactId>
    <version>2.2.1</version>

<!--web依赖-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.2.5.RELEASE</version>
</dependency>

rocketmq:
  name-server: 192.168.200.144:9876 #服务器ip:nameServer端口
  producer:
    group: sanyouProducer

@RestController
@Slf4j
public class RocketMQDelayTaskController {

    @Resource
    private DefaultMQProducer producer;

    @GetMapping("/rocketmq/add")
    public void addTask(@RequestParam("task") String task) throws Exception {
        Message msg = new Message("sanyouDelayTaskTopic", "TagA", task.getBytes(RemotingHelper.DEFAULT_CHARSET));
        msg.setDelayTimeLevel(2);
        // 发送消息并得到消息的发送结果，然后打印
        log.info("提交延迟任务");
        producer.send(msg);
    }

}

@Component
@RocketMQMessageListener(consumerGroup = "sanyouConsumer", topic = "sanyouDelayTaskTopic")
@Slf4j
public class SanYouDelayTaskTopicListener implements RocketMQListener<String> {

    @Override
    public void onMessage(String msg){
        log.info("获取到延迟任务:{}", msg);
    }

}

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-amqp</artifactId>
    <version>2.2.5.RELEASE</version>
</dependency>

spring:
  rabbitmq:
    host: 192.168.200.144 #服务器ip
    port: 5672
    virtual-host: /

@Configuration
public class RabbitMQConfiguration {

    @Bean
    public DirectExchange sanyouDirectExchangee(){
        return new DirectExchange("sanyouDirectExchangee");
    }

    @Bean
    public Queue sanyouQueue(){
        return QueueBuilder
                //指定队列名称，并持久化
                .durable("sanyouQueue")
                //设置队列的超时时间为5秒，也就是延迟任务的时间
                .ttl(5000)
                //指定死信交换机
                .deadLetterExchange("sanyouDelayTaskExchangee")
                .build();
    }

    @Bean
    public Binding sanyouQueueBinding(){
        return BindingBuilder.bind(sanyouQueue()).to(sanyouDirectExchangee()).with("");
    }

    @Bean
    public DirectExchange sanyouDelayTaskExchange(){
        return new DirectExchange("sanyouDelayTaskExchangee");
    }

    @Bean
    public Queue sanyouDelayTaskQueue(){
        return QueueBuilder
                //指定队列名称，并持久化
                .durable("sanyouDelayTaskQueue")
                .build();
    }

    @Bean
    public Binding sanyouDelayTaskQueueBinding(){
        return BindingBuilder.bind(sanyouDelayTaskQueue()).to(sanyouDelayTaskExchange()).with("");
    }

}

@RestController
@Slf4j
public class RabbitMQDelayTaskController {

    @Resource
    private RabbitTemplate rabbitTemplate;

    @GetMapping("/rabbitmq/add")
    public void addTask(@RequestParam("task") String task) throws Exception {
        // 消息ID，需要封装到CorrelationData中
        CorrelationData correlationData = new CorrelationData(UUID.randomUUID().toString());
        log.info("提交延迟任务");
        // 发送消息
        rabbitTemplate.convertAndSend("sanyouDirectExchangee", "", task, correlationData);
    }

}