14 Spring Boot 定时任务

@EnableScheduling

首先在 SpringBoot 启动类加上 @EnableScheduling 启用定时任务。

@SpringBootApplication
@EnableScheduling
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}

创建 scheduled task

使用 @Scheduled 注解就能很方便地创建一个定时任务,下面的代码中涵盖了 @Scheduled 的常见用法,包括:固定速率执行、固定延迟执行、初始延迟执行、使用 Cron 表达式执行定时任务。

在线 Cron 表达式生成器

@Slf4j
@Component
public class ScheduledTasks {
private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
/**
* fixedRate:固定速率执行。每5秒执行一次。
*/
@Scheduled(fixedRate = 5000)
public void reportCurrentTimeWithFixedRate() {
log.info("Current Thread : {}", Thread.currentThread().getName());
log.info("Fixed Rate Task : The time is now {}", dateFormat.format(new Date()));
}
/**
* fixedDelay:固定延迟执行。距离上一次调用成功后2秒才执。
*/
@Scheduled(fixedDelay = 2000)
public void reportCurrentTimeWithFixedDelay() {
try {
TimeUnit.SECONDS.sleep(3);
log.info("Fixed Delay Task : The time is now {}", dateFormat.format(new Date()));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/**
* initialDelay:初始延迟。任务的第一次执行将延迟5秒,然后将以5秒的固定间隔执行。
*/
@Scheduled(initialDelay = 5000, fixedRate = 5000)
public void reportCurrentTimeWithInitialDelay() {
log.info("Fixed Rate Task with Initial Delay : The time is now {}", dateFormat.format(new Date()));
}
/**
* cron:使用Cron表达式。 每分钟的1,2秒运行
*/
@Scheduled(cron = "1-2 * * * * ? ")
public void reportCurrentTimeWithCronExpression() {
log.info("Cron Expression: The time is now {}", dateFormat.format(new Date()));
}
}

注意 fixedRate 模式有个小坑,假如有这样一种情况:某个方法的定时器设定的固定速率是每 5 秒执行一次。这个方法现在要执行下面四个任务,四个任务的耗时是:6 s、6s、2s、3s,请问这些任务默认情况下(单线程)将如何被执行?程序验证:

@Component
@Slf4j
public class ScheduledTasks {
private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
private List<Integer> index = Arrays.asList(6, 6, 2, 3);
int i = 0;
@Scheduled(fixedRate = 5000)
public void reportCurrentTimeWithFixedRate() {
if (i == 0) {
log.info("Start time is {}", dateFormat.format(new Date()));
}
if (i < 5) {
try {
TimeUnit.SECONDS.sleep(index.get(i));
log.info("Fixed Rate Task : The time is now {}", dateFormat.format(new Date()));
} catch (InterruptedException e) {
e.printStackTrace();
}
i++;
}
}
}

运行程序输出如下:

Start time is 09:26:41
Fixed Rate Task : The time is now 09:26:47
Fixed Rate Task : The time is now 09:26:53
Fixed Rate Task : The time is now 09:26:55
Fixed Rate Task : The time is now 09:26:59

示意图:

fixedRate

自定义线程池

默认情况下,@Scheduled 任务都在 Spring 创建的大小为 1 的默认线程池中执行,你可以通过在加了 @Scheduled 注解的方法里加上下面这段代码来验证。

log.info("Current Thread : {}", Thread.currentThread().getName());

每次运行都会输出:

Current Thread : scheduling-1

如果需要自定义线程池执行话只需要新加一个实现 SchedulingConfigurer 接口的 configureTasks 的类即可,这个类需要加上 @Configuration 注解。

@Configuration
public class SchedulerConfig implements SchedulingConfigurer {
private final int POOL_SIZE = 10;
@Override
public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
ThreadPoolTaskScheduler threadPoolTaskScheduler = new ThreadPoolTaskScheduler();
threadPoolTaskScheduler.setPoolSize(POOL_SIZE);
threadPoolTaskScheduler.setThreadNamePrefix("my-scheduled-task-pool-");
threadPoolTaskScheduler.initialize();
scheduledTaskRegistrar.setTaskScheduler(threadPoolTaskScheduler);
}
}

并发执行

测试代码:

@Slf4j
@Component
public class ScheduledTasks {
private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
@Scheduled(fixedDelay = 2000)
public void reportCurrentTimeWithFixedDelay() {
try {
TimeUnit.SECONDS.sleep(3);
log.info("Fixed Delay Task : The time is now {}", dateFormat.format(new Date()));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

reportCurrentTimeWithFixedDelay() 方法会每 5 秒执行一次,执行代码输出如下:

[scheduling-1] : Fixed Delay Task : The time is now 09:45:12
[scheduling-1] : Fixed Delay Task : The time is now 09:45:17
[scheduling-1] : Fixed Delay Task : The time is now 09:45:22
[scheduling-1] : Fixed Delay Task : The time is now 09:45:27
[scheduling-1] : Fixed Delay Task : The time is now 09:45:32
[scheduling-1] : Fixed Delay Task : The time is now 09:45:37

添加 @EnableAsync@Async 这两个注解让任务并行执行:

@Slf4j
@EnableAsync
@Component
public class ScheduledTasks {
private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
@Async
@Scheduled(fixedDelay = 2000)
public void reportCurrentTimeWithFixedDelay() {
/* .... */
}
}

reportCurrentTimeWithFixedDelay() 方法上加上 @Async 注解后会每 2 秒执行一次,执行代码输出如下:

[lTaskExecutor-1] : Fixed Delay Task : The time is now 09:44:04
[lTaskExecutor-2] : Fixed Delay Task : The time is now 09:44:06
[lTaskExecutor-3] : Fixed Delay Task : The time is now 09:44:08
[lTaskExecutor-4] : Fixed Delay Task : The time is now 09:44:10
[lTaskExecutor-5] : Fixed Delay Task : The time is now 09:44:12
[lTaskExecutor-6] : Fixed Delay Task : The time is now 09:44:14