Springboot @Scheduled实现原理
文章目录
- 实现原理
-
- 1.开启计划任务
-
- ScheduledAnnotationBeanPostProcessor
- 2.创建任务并放入到任务列表
-
- 依次加载所有的实现Scheduled注解的类方法
- 将对应类型的定时器放入相应的定时任务列表中
- 3.执行定时任务
-
- 任务列表提交到线程池，任务开始定时执行
- 定时任务线程池执行原理
- 注意事项
实现原理
1.开启计划任务
@EnableScheduling注解用于开启计划任务。
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Import({SchedulingConfiguration.class})
@Documented
public @interface EnableScheduling {
}
@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class SchedulingConfiguration {
@Bean(name = TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public ScheduledAnnotationBeanPostProcessor scheduledAnnotationProcessor() {
return new ScheduledAnnotationBeanPostProcessor();
}
}
通过@Import引入了SchedulingConfiguration这个配置类，使这个配置类生效。向spring容器中注入了一个bean:ScheduledAnnotationBeanPostProcessor。
ScheduledAnnotationBeanPostProcessor
-
ScheduledAnnotationBeanPostProcessor主要实现了两个接口
- DestructionAwareBeanPostProcessor
- ApplicationListener
-
ScheduledAnnotationBeanPostProcessor间接继承了BeanPostProcessor类
2.创建任务并放入到任务列表
spring在初始化bean后，通过ScheduledAnnotationBeanPostProcessor的postProcessAfterInitialization方法拦截到所有的用到@Scheduled注解的方法，并解析相应的的注解参数，放入“定时任务列表”等待后续处理
@Scheduled注解配置可参考文章：@Scheduled注解详解
依次加载所有的实现Scheduled注解的类方法
ScheduledAnnotationBeanPostProcessor的postProcessAfterInitialization方法
@Override
public Object postProcessAfterInitialization(final Object bean, String beanName) {
Class<?> targetClass = AopProxyUtils.ultimateTargetClass(bean);
if (!this.nonAnnotatedClasses.contains(targetClass)) {
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: " + bean.getClass());
}
}
else {
// Non-empty set of methods
annotatedMethods.forEach((method, scheduledMethods) ->
scheduledMethods.forEach(scheduled -> processScheduled(scheduled, method, bean)));
if (logger.isDebugEnabled()) {
logger.debug(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
"': " + annotatedMethods);
}
}
}
return bean;
}
遍历了每个bean的方法，并找出使用了@Scheduled的方法，调用processScheduled进行处理。
将对应类型的定时器放入相应的定时任务列表中
ScheduledAnnotationBeanPostProcessor的processScheduled方法
protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
try {
Assert.isTrue(method.getParameterCount() == 0,
"Only no-arg methods may be annotated with @Scheduled");
Method invocableMethod = AopUtils.selectInvocableMethod(method, bean.getClass());
Runnable runnable = new ScheduledMethodRunnable(bean, invocableMethod);
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;
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> registeredTasks = this.scheduledTasks.get(bean);
if (registeredTasks == null) {
registeredTasks = new LinkedHashSet<>(4);
this.scheduledTasks.put(bean, registeredTasks);
}
registeredTasks.addAll(tasks);
}
}
catch (IllegalArgumentException ex) {
throw new IllegalStateException(
"Encountered invalid @Scheduled method '" + method.getName() + "': " + ex.getMessage());
}
}
解析@Scheduled注解传进来的参数（cron表达式或者延时等）并创建不同类型的任务提交到registrar中，registrar是用来注册要放到计划任务线程池中运行的任务的，它里面包含一个线程池和任务列表，这一步只是放到了列表中。
现在@Scheduled已经被解析，并转成了Runable任务对像放到了ScheduledTaskRegistrar对像中了，现在就差把它们放到线程池中启动了。
3.执行定时任务
任务列表提交到线程池，任务开始定时执行
ScheduledAnnotationBeanPostProcessor实现了ApplicationListener的接口。
当Spring容器初始化完成会触发ContextRefreshedEvent事件，调用ScheduledAnnotationBeanPostProcessor的onApplicationEvent方法，方法调用finishRegistration完成任务列表注册到线程池，任务开始定时执行。
public void onApplicationEvent(ContextRefreshedEvent event) {
if (event.getApplicationContext() == this.applicationContext) {
this.finishRegistration();
}
}
private void finishRegistration() {
if (this.scheduler != null) {
this.registrar.setScheduler(this.scheduler);
}
if (this.beanFactory instanceof ListableBeanFactory) {
Map<String, SchedulingConfigurer> beans =
((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);
List<SchedulingConfigurer> configurers = new ArrayList<>(beans.values());
AnnotationAwareOrderComparator.sort(configurers);
for (SchedulingConfigurer configurer : configurers) {
configurer.configureTasks(this.registrar);
}
}
if (this.registrar.hasTasks() && this.registrar.getScheduler() == null) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to find scheduler by type");
try {
// Search for TaskScheduler bean...
this.registrar.setTaskScheduler(resolveSchedulerBean(beanFactory, TaskScheduler.class, false));
}
catch (NoUniqueBeanDefinitionException ex) {
logger.debug("Could not find unique TaskScheduler bean", ex);
try {
this.registrar.setTaskScheduler(resolveSchedulerBean(beanFactory, TaskScheduler.class, true));
}
catch (NoSuchBeanDefinitionException ex2) {
if (logger.isInfoEnabled()) {
logger.info("More than one TaskScheduler bean exists within the context, and " +
"none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' " +
"(possibly as an alias); or implement the SchedulingConfigurer interface and call " +
"ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " +
ex.getBeanNamesFound());
}
}
}
catch (NoSuchBeanDefinitionException ex) {
logger.debug("Could not find default TaskScheduler bean", ex);
// Search for ScheduledExecutorService bean next...
try {
this.registrar.setScheduler(resolveSchedulerBean(beanFactory, ScheduledExecutorService.class, false));
}
catch (NoUniqueBeanDefinitionException ex2) {
logger.debug("Could not find unique ScheduledExecutorService bean", ex2);
try {
this.registrar.setScheduler(resolveSchedulerBean(beanFactory, ScheduledExecutorService.class, true));
}
catch (NoSuchBeanDefinitionException ex3) {
if (logger.isInfoEnabled()) {
logger.info("More than one ScheduledExecutorService bean exists within the context, and " +
"none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' " +
"(possibly as an alias); or implement the SchedulingConfigurer interface and call " +
"ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " +
ex2.getBeanNamesFound());
}
}
}
catch (NoSuchBeanDefinitionException ex2) {
logger.debug("Could not find default ScheduledExecutorService bean", ex2);
// Giving up -> falling back to default scheduler within the registrar...
logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");
}
}
}
this.registrar.afterPropertiesSet();
}
-
找到SchedulingConfigurer接口的所有所有实现类，调用它的configureTasks方法
通常我们可以自定义一个类实现SchedulingConfigurer，并对registrar里面的属性赋值，最常用的做法是自定线程池注入到registrar中，因为registrar默认是单线程的线程池，也即是说@Scheduled方法是串行的
-
对ScheduledTaskRegistrar对像中的TaskScheduler属性赋值
TaskScheduler这个属性即是线程池对像，如果在第一步我们已经自己指定了一个线程池，这部分代码会跳过。
-
调用this.registrar.afterPropertiesSet()
这一步很重要，它的功能就是把所有任务提交到线程池中。
@Override public void afterPropertiesSet() { scheduleTasks(); } /** * Schedule all registered tasks against the underlying * {@linkplain #setTaskScheduler(TaskScheduler) task scheduler}. */ @SuppressWarnings("deprecation") protected 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)); } } }ScheduledThreadPoolExecutor的run方法
//说明：每次执行定时任务结束后，会先设置下下次定时任务的执行时间，以此来确认下次任务的执行时间。 public void run() { boolean periodic = isPeriodic(); if (!canRunInCurrentRunState(periodic)) cancel(false); else if (!periodic) ScheduledFutureTask.super.run(); else if (ScheduledFutureTask.super.runAndReset()) { setNextRunTime(); reExecutePeriodic(outerTask); } }- 首先判断线程池是否为空，如果是空，就新建
一个单线程的线程池； - 先执行corn，计算出相应的下次执行时间，放入线程池中。再执行fixedRate，计算出相应的下次执行时间，放入线程池中。
- 线程池中某一任务到达执行时间，开始执行，执行完成后会先设置下次定时任务的执行时间，放到线程池中。
- 首先判断线程池是否为空，如果是空，就新建
到这一步，@Scheduled作用生效，方法将会定时执行了。
定时任务线程池执行原理
定时任务使用的一般是ScheduledThreadPoolExecutor线程池
该类型线程池解析见该文章：Java线程池解析
注意事项
- 任务默认是单线程执行，前一个任务执行完毕，才会继续执行下一个任务。所以上一个任务一直未完成，会导致后面的任务全部“失效”。
- 如果多个定时任务定义的是同一个时间，那么也是顺序执行的，会根据程序加载Scheduled方法的先后来执行。先执行cron，之后再执行fixedRate。