SpringBoot定时任务@Scheduled注解详解

Bertha 。 2024-03-26 20:56 127阅读 0赞

### SpringBoot定时任务@Scheduled注解详解 ###

*  项目开发中，经常会遇到定时任务的场景，Spring提供了`@Scheduled注解`，方便进行定时任务的开发

### 概述 ###

*  要使用`@Scheduled`注解，首先需要在启动类添加`@EnableScheduling`，启用Spring的计划任务执行功能，这样可以在容器中的任何Spring管理的bean上检测`@Scheduled`注解，执行计划任务

### 注解定义 ###

*      @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
        @Retention(RetentionPolicy.RUNTIME)
        @Documented
        @Repeatable(Schedules.class)
        public @interface Scheduled {
        
            String cron() default "";
        
            String zone() default "";
        
            long fixedDelay() default -1;
        
            String fixedDelayString() default "";
        
            long fixedRate() default -1;
        
            String fixedRateString() default "";
            
            long initialDelay() default -1;
        
            String initialDelayString() default "";
        
        }

### 参数说明 ###

*  ![5b9a2948163346689e69794e4fd44989.png][]

### 源码解析 ###

*  配置了`@Scheduled`注解的方法，Spring的处理是通过注册ScheduledAnnotationBeanPostProcessor来执行，将不同配置参数的任务分配给不同的handler处理，核心代码如下
 *  org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor\#postProcessAfterInitialization
 *      @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) {
            if (bean instanceof AopInfrastructureBean || bean instanceof TaskScheduler ||
                    bean instanceof ScheduledExecutorService) {
                // Ignore AOP infrastructure such as scoped proxies.
                return bean;
            }
        
            Class<?> targetClass = AopProxyUtils.ultimateTargetClass(bean);
            if (!this.nonAnnotatedClasses.contains(targetClass) &&
                    AnnotationUtils.isCandidateClass(targetClass, Arrays.asList(Scheduled.class, Schedules.class))) {
                Map<Method, Set<Scheduled>> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
                        (MethodIntrospector.MetadataLookup<Set<Scheduled>>) method -> {
                            Set<Scheduled> scheduledMethods = AnnotatedElementUtils.getMergedRepeatableAnnotations(
                                    method, Scheduled.class, Schedules.class);
                            return (!scheduledMethods.isEmpty() ? scheduledMethods : null);
                        });
                if (annotatedMethods.isEmpty()) {
                    this.nonAnnotatedClasses.add(targetClass);
                    if (logger.isTraceEnabled()) {
                        logger.trace("No @Scheduled annotations found on bean class: " + targetClass);
                    }
                }
                else {
                    // Non-empty set of methods
                    annotatedMethods.forEach((method, scheduledMethods) ->
                            scheduledMethods.forEach(scheduled -> processScheduled(scheduled, method, bean)));
                    if (logger.isTraceEnabled()) {
                        logger.trace(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
                                "': " + annotatedMethods);
                    }
                }
            }
            return bean;
        }
        
 *  org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor\#processScheduled
 *      /**
         * Process the given {@code @Scheduled} method declaration on the given bean.
         * @param scheduled the @Scheduled annotation
         * @param method the method that the annotation has been declared on
         * @param bean the target bean instance
         * @see #createRunnable(Object, Method)
         */
        protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
            try {
                Runnable runnable = createRunnable(bean, method);
                boolean processedSchedule = false;
                String errorMessage =
                        "Exactly one of the 'cron', 'fixedDelay(String)', or 'fixedRate(String)' attributes is required";
                Set<ScheduledTask> tasks = new LinkedHashSet<>(4);
                // Determine initial delay
                long initialDelay = scheduled.initialDelay();
                String initialDelayString = scheduled.initialDelayString();
                if (StringUtils.hasText(initialDelayString)) {
                    Assert.isTrue(initialDelay < 0, "Specify 'initialDelay' or 'initialDelayString', not both");
                    if (this.embeddedValueResolver != null) {
                        initialDelayString = this.embeddedValueResolver.resolveStringValue(initialDelayString);
                    }
                    if (StringUtils.hasLength(initialDelayString)) {
                        try {
                            initialDelay = parseDelayAsLong(initialDelayString);
                        }
                        catch (RuntimeException ex) {
                            throw new IllegalArgumentException(
                                    "Invalid initialDelayString value \"" + initialDelayString + "\" - cannot parse into long");
                        }
                    }
                }
                // Check cron expression
                String cron = scheduled.cron();
                if (StringUtils.hasText(cron)) {
                    String zone = scheduled.zone();
                    if (this.embeddedValueResolver != null) {
                        cron = this.embeddedValueResolver.resolveStringValue(cron);
                        zone = this.embeddedValueResolver.resolveStringValue(zone);
                    }
                    if (StringUtils.hasLength(cron)) {
                        Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
                        processedSchedule = true;
                        if (!Scheduled.CRON_DISABLED.equals(cron)) {
                            TimeZone timeZone;
                            if (StringUtils.hasText(zone)) {
                                timeZone = StringUtils.parseTimeZoneString(zone);
                            }
                            else {
                                timeZone = TimeZone.getDefault();
                            }
                            tasks.add(this.registrar.scheduleCronTask(new CronTask(runnable, new CronTrigger(cron, timeZone))));
                        }
                    }
                }
                // At this point we don't need to differentiate between initial delay set or not anymore
                if (initialDelay < 0) {
                    initialDelay = 0;
                }
                // Check fixed delay
                long fixedDelay = scheduled.fixedDelay();
                if (fixedDelay >= 0) {
                    Assert.isTrue(!processedSchedule, errorMessage);
                    processedSchedule = true;
                    tasks.add(this.registrar.scheduleFixedDelayTask(new FixedDelayTask(runnable, fixedDelay, initialDelay)));
                }
                String fixedDelayString = scheduled.fixedDelayString();
                if (StringUtils.hasText(fixedDelayString)) {
                    if (this.embeddedValueResolver != null) {
                        fixedDelayString = this.embeddedValueResolver.resolveStringValue(fixedDelayString);
                    }
                    if (StringUtils.hasLength(fixedDelayString)) {
                        Assert.isTrue(!processedSchedule, errorMessage);
                        processedSchedule = true;
                        try {
                            fixedDelay = parseDelayAsLong(fixedDelayString);
                        }
                        catch (RuntimeException ex) {
                            throw new IllegalArgumentException(
                                    "Invalid fixedDelayString value \"" + fixedDelayString + "\" - cannot parse into long");
                        }
                        tasks.add(this.registrar.scheduleFixedDelayTask(new FixedDelayTask(runnable, fixedDelay, initialDelay)));
                    }
                }
                // Check fixed rate
                long fixedRate = scheduled.fixedRate();
                if (fixedRate >= 0) {
                    Assert.isTrue(!processedSchedule, errorMessage);
                    processedSchedule = true;
                    tasks.add(this.registrar.scheduleFixedRateTask(new FixedRateTask(runnable, fixedRate, initialDelay)));
                }
                String fixedRateString = scheduled.fixedRateString();
                if (StringUtils.hasText(fixedRateString)) {
                    if (this.embeddedValueResolver != null) {
                        fixedRateString = this.embeddedValueResolver.resolveStringValue(fixedRateString);
                    }
                    if (StringUtils.hasLength(fixedRateString)) {
                        Assert.isTrue(!processedSchedule, errorMessage);
                        processedSchedule = true;
                        try {
                            fixedRate = parseDelayAsLong(fixedRateString);
                        }
                        catch (RuntimeException ex) {
                            throw new IllegalArgumentException(
                                    "Invalid fixedRateString value \"" + fixedRateString + "\" - cannot parse into long");
                        }
                        tasks.add(this.registrar.scheduleFixedRateTask(new FixedRateTask(runnable, fixedRate, initialDelay)));
                    }
                }
                // Check whether we had any attribute set
                Assert.isTrue(processedSchedule, errorMessage);
                // Finally register the scheduled tasks
                synchronized (this.scheduledTasks) {
                    Set<ScheduledTask> regTasks = this.scheduledTasks.computeIfAbsent(bean, key -> new LinkedHashSet<>(4));
                    regTasks.addAll(tasks);
                }
            }
            catch (IllegalArgumentException ex) {
                throw new IllegalStateException(
                        "Encountered invalid @Scheduled method '" + method.getName() + "': " + ex.getMessage());
            }
        }
 *  org.springframework.scheduling.config.ScheduledTaskRegistrar\#scheduleTasks
 *      /**
         * Schedule all registered tasks against the underlying
         * {@linkplain #setTaskScheduler(TaskScheduler) task scheduler}.
         */
        proected void scheduleTasks() {
            if (this.taskScheduler == null) {
                this.localExecutor = Executors.newSingleThreadScheduledExecutor();
                this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
            }
            if (this.triggerTasks != null) {
                for (TriggerTask task : this.triggerTasks) {
                    addScheduledTask(scheduleTriggerTask(task));
                }
            }
            if (this.cronTasks != null) {
                for (CronTask task : this.cronTasks) {
                    addScheduledTask(scheduleCronTask(task));
                }
            }
            if (this.fixedRateTasks != null) {
                for (IntervalTask task : this.fixedRateTasks) {
                    addScheduledTask(scheduleFixedRateTask(task));
                }
            }
            if (this.fixedDelayTasks != null) {
                for (IntervalTask task : this.fixedDelayTasks) {
                    addScheduledTask(scheduleFixedDelayTask(task));
                }
            }
        }

### 使用详解 ###

#### 定时任务同步/异步执行 ####

*  定时任务执行默认是单线程模式，会创建一个本地线程池，线程池大小为1。当项目中有多个定时任务时，任务之间会相互等待，同步执行
 *  源码:
 *      // org.springframework.scheduling.config.ScheduledTaskRegistrar#scheduleTasks
        if (this.taskScheduler == null) {
            this.localExecutor = Executors.newSingleThreadScheduledExecutor();
            this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
        }
        
        // java.util.concurrent.Executors#newSingleThreadScheduledExecutor()
        public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
            return new DelegatedScheduledExecutorService
                (new ScheduledThreadPoolExecutor(1));
        }
    
        
 *  代码示例:
 *      @Slf4j
        @Component
        public class RunIntervalTestScheduler {
        
            @Scheduled(cron = "0/1 * * * * ?")
            public void singleThreadTest1() {
                log.info("singleThreadTest1");
                LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
            }
        
            @Scheduled(cron = "0/1 * * * * ?")
            public void singleThreadTest2() {
                log.info("singleThreadTest2");
                LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
            }
        
            @Scheduled(cron = "0/1 * * * * ?")
            public void singleThreadTest3() {
                log.info("singleThreadTest3");
                LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
            }
        }
        
 *  执行结果:
 *  ![40d4d56996e24ec6a6552dc0bfc6f4fc.png][]
 *  可以看到，默认情况下，三个任务串行执行，都使用`pool-1-thread-1`同一个线程池，并且线程只有一个
 *  可以通过实现`SchedulingConfigurer`接口，手动创建线程池，配置期望的线程数量
 *  示例代码:
 *      @Configuration
        public class ScheduledConfig implements SchedulingConfigurer {
        
            /**
             * 任务执行线程池大小
             */
            private static final int TASK_POOL_SIZE = 50;
            /**
             * 线程名
             */
            private static final String TASK_THREAD_PREFIX = "test-task-";
        
            @Override
            public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
                ThreadPoolTaskScheduler taskPool = new ThreadPoolTaskScheduler();
                taskPool.setPoolSize(TASK_POOL_SIZE);
                taskPool.setThreadNamePrefix(TASK_THREAD_PREFIX);
                taskPool.initialize();
                scheduledTaskRegistrar.setTaskScheduler(taskPool);
            }
        }
        
 *  任务执行结果:
 *  ![58472fe68140441d8e5e858b187fbf55.png][]
 *  此时任务的执行已经异步化，从自定义线程池中分配线程执行任务，在实际应用中需要考虑实际任务数量，创建相应大小的线程池

#### fixedRate/fixedDelay区别 ####

*  fixedRate是配置上一次任务执行开始到下一次执行开始的间隔时间，不会等待上一次任务执行完成就会调度下一次任务，将其放入等待队列中
 *  代码示例:
 *      @Slf4j
        @Component
        public class RunIntervalTestScheduler {
        
            @Scheduled(initialDelay = 1000, fixedRate = 1000)
            public void fixedRate() throws Exception {
                log.info("fixedRate run");
                TimeUnit.SECONDS.sleep(3);
            }
        
        }
    
        
 *  执行结果:
 *  ![4214d91b66d143fbba86ac3dd7001d80.png][]
 *  任务配置的fixedRate为1s，执行日志打印的时间间隔都是3s左右，也就是上一次执行完成后，紧接着就执行下一次任务
 *  fixedDelay是配置的上一次任务执行结束到下一次执行开始的间隔时间，也就是说会等待上一次任务执行结束后，延迟间隔时间，再执行下一次任务
 *  代码示例:
 *      @Slf4j
        @Component
        public class RunIntervalTestScheduler {
        
            @Scheduled(initialDelay = 1000, fixedDelay = 1000)
            public void fixedDelay() throws Exception {
                log.info("fixedDelay run");
                TimeUnit.SECONDS.sleep(3);
            }
        
        }
 *  执行结果:
 *  ![1b7b1f27d88b4c928a08992ea040bfe7.png][]
 *  任务配置的fixedDelay为1s，执行日志打印的时间间隔都是4s左右，也就是上一次执行完成后，延迟1s后执行下一次任务
 *  cron表达式如果配置为类似每秒执行、每分钟执行(例:0/1 \* \* \* \* ?, 每秒执行)，调度跟fixedDelay是一致的，也是在上一次任务执行结束后，等待间隔时间
 *  代码示例:
 *      @Slf4j
        @Component
        public class RunIntervalTestScheduler {
        
            @Scheduled(cron = "0/1 * * * * ?")
            public void cronRun() throws Exception{
                log.info("cron run");
                TimeUnit.SECONDS.sleep(3);
            }
        
        }
 *  执行结果:
 *  ![d3b0e219c1e84a41b0c1f6191346b602.png][]
 *  执行日志打印的时间间隔都是4s左右，也就是上一次执行完成后，延迟1s后执行下一次任务
 *  cron表达式如果配置为固定时间执行(例:1 \* \* \* \* ?, 秒数为1时执行)，若上一次任务没有执行完，则不会调度本次任务，跳过本次执行，等待下一次执行周期
 *  代码示例:
 *      @Slf4j
        @Component
        public class RunIntervalTestScheduler {
        
            @Scheduled(cron = "1 * * * * ?")
            public void cronRun() throws Exception{
                log.info("cron run");
                TimeUnit.SECONDS.sleep(70);
            }
        
        }
        
 *  执行结果:
 *  ![8d793ad5a5e5485e8ff948e3eb48f28b.png][]
 *  上一次任务未执行完毕，则跳过了本次执行

[5b9a2948163346689e69794e4fd44989.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/47c1453268424ef8a671366b89714569.png
[40d4d56996e24ec6a6552dc0bfc6f4fc.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/73d2eee23aba40e69a37d1de0969cecd.png
[58472fe68140441d8e5e858b187fbf55.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/9f80e9dc9e20459c948fbebe22a38baf.png
[4214d91b66d143fbba86ac3dd7001d80.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/87ce56ce76374b8fbc795758bf25364e.png
[1b7b1f27d88b4c928a08992ea040bfe7.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/522da3d41822407ba766677ed960b45f.png
[d3b0e219c1e84a41b0c1f6191346b602.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/a52fa7a97ae3463482c82d5af187c433.png
[8d793ad5a5e5485e8ff948e3eb48f28b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/9163a4e8f6144491ba4b783daced4c14.png