27.【Spring源码分析】27-基于注解@Scheduled定时任务实现
27.【Spring源码分析】27-基于注解@Scheduled定时任务实现
1、概述
@EnableScheduling启用Spring的定时任务功能，这允许检测容器中@Scheduled注释的bean。执行定时任务还需要一个调度器TaskScheduler，默认情况下，将在容器中搜索一个关联的scheduler定义：要么是一个唯一的TaskScheduler类型的bean，要么是一个bean name是taskScheduler的TaskScheduler。这两种查找的都是。ScheduledExecutorService。如果这两种查找方式都没有，则默认使用一个单线程的调度器。实现SchedulingConfigurer}允许细粒度通过ScheduledTaskRegistrar控制任务注册。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {}
@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class SchedulingConfiguration {
//bean name=org.springframework.context.annotation.internalScheduledAnnotationProcessor
@Bean(name = TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public ScheduledAnnotationBeanPostProcessor scheduledAnnotationProcessor() {
return new ScheduledAnnotationBeanPostProcessor();
}
}2、寻找定时任务方法
ScheduledAnnotationBeanPostProcessor会查找任何带有@Scheduled的方法。
@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)) {
//找出所有的@Scheduled方法
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) ->
//将每个@Scheduled方法转换成一个Task对象注册到ScheduledTaskRegistrar中
scheduledMethods.forEach(scheduled -> processScheduled(scheduled, method, bean)));
if (logger.isTraceEnabled()) {
logger.trace(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
"': " + annotatedMethods);
}
}
}
return bean;
}上面代码调用processScheduled()方法将@Schedule方法注册一个ScheduledTaskRegistrar对象中，在分析具体如何注册之前先看看ScheduledTaskRegistrar的机构。
public class ScheduledTaskRegistrar implements ScheduledTaskHolder, InitializingBean, DisposableBean {
//负责执行任务
@Nullable
private TaskScheduler taskScheduler;
//没有设置taskScheduler默认使用Executors.newSingleThreadScheduledExecutor()
@Nullable
private ScheduledExecutorService localExecutor;
//@Scheduled方法默认不会进入这个容器，但是可自己添加
@Nullable
private List<TriggerTask> triggerTasks;
//检测到CronTask类型的任务
@Nullable
private List<CronTask> cronTasks;
//检测到FixedRateTask类型的任务
@Nullable
private List<IntervalTask> fixedRateTasks;
//检测到FixedDelayTask类型的任务
@Nullable
private List<IntervalTask> fixedDelayTasks;
//还未触发的任务
private final Map<Task, ScheduledTask> unresolvedTasks = new HashMap<>(16);
//已触发过的任务
private final Set<ScheduledTask> scheduledTasks = new LinkedHashSet<>(16);
}以上就是不同类型任务会放入不同的容器中，等到任务触发的时候从容器中取出。
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());
}
}以上就是不同类型的任务注册，我们拿CronTask举例看其具体注册过程。
@Nullable
public ScheduledTask scheduleCronTask(CronTask task) {
ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
boolean newTask = false;
if (scheduledTask == null) {
scheduledTask = new ScheduledTask(task);
//代表之前未注册过
newTask = true;
}
//如果taskScheduler!=null，直接执行,之前未注册过也不会加入容器中
if (this.taskScheduler != null) {
scheduledTask.future = this.taskScheduler.schedule(task.getRunnable(), task.getTrigger());
}
else {
addCronTask(task);
this.unresolvedTasks.put(task, scheduledTask);
}
return (newTask ? scheduledTask : null);
}scheduleCronTask()这个方法有两层含义：注册或执行。在taskScheduler还没有准备好时负责注册任务，什么时候会注册好呢，后面会分析。之所以要兼顾注册和执行，是因为可能有些定时任务bean是在容器完全启动后加入容器中的。
3、触发定时任务
有三种方式可以触发任务，一个是上面讲到的在检测@Schedule方法的时候，一个是在afterSingletonsInstantiated()方法执行的时候，一个是在接收到ContextRefreshedEvent事件的时候。其实这三种触发任务的时机最后都是调用上面这个scheduleCronTask()方法，而这个方法真正执行任务又需要scheduler!=null。那么这个scheduler是何时被赋值的呢？
afterSingletonsInstantiated()和onApplicationEvent()方法执行的时候都会调用同一个方法finishRegistration()，这个方法会为registrar设置一个TaskScheduler的。
@Override
public void afterSingletonsInstantiated() {
// Remove resolved singleton classes from cache
this.nonAnnotatedClasses.clear();
if (this.applicationContext == null) {
// Not running in an ApplicationContext -> register tasks early...
finishRegistration();
}
}
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
if (event.getApplicationContext() == this.applicationContext) {
// Running in an ApplicationContext -> register tasks this late...
// giving other ContextRefreshedEvent listeners a chance to perform
// their work at the same time (e.g. Spring Batch's job registration).
finishRegistration();
}
}
private void finishRegistration() {
if (this.scheduler != null) {
this.registrar.setScheduler(this.scheduler);
}
if (this.beanFactory instanceof ListableBeanFactory) {
//这里提供了一个机会可以实现自定义SchedulingConfigurer来配置registrar
//譬如注册新任务，设置一个TaskScheduler
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);
}
}
//如果已经有任务注册了但是还没有TaskScheduler，则会调用resolveSchedulerBean()方法寻找一个TaskScheduler
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(this.beanFactory, TaskScheduler.class, false));
}
catch (NoUniqueBeanDefinitionException ex) {
logger.trace("Could not find unique TaskScheduler bean", ex);
try {
this.registrar.setTaskScheduler(resolveSchedulerBean(this.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.trace("Could not find default TaskScheduler bean", ex);
// Search for ScheduledExecutorService bean next...
try {
this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, false));
}
catch (NoUniqueBeanDefinitionException ex2) {
logger.trace("Could not find unique ScheduledExecutorService bean", ex2);
try {
this.registrar.setScheduler(resolveSchedulerBean(this.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.trace("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");
}
}
}
//触发所有未触发过的任务
this.registrar.afterPropertiesSet();
}看上面代码最后一行就是开头说三种触发任务的时机后两种，触发任务前还会检测是否已经有了scheduler，如果没有则调用resolveSchedulerBean()方法从容器返回一个，如果容器中TaskScheduler实例不止一个则尝试取bean name是taskScheduler。如果没有类型是TaskScheduler的，则尝试取类型是ScheduledExecutorService，不止一个的话依然取名字是taskScheduler的，返回的是ScheduledExecutorService实例，会在this.registrar.setScheduler()方法中使用ConcurrentTaskScheduler将其包装成TaskScheduler如下：
public void setTaskScheduler(TaskScheduler taskScheduler) {
Assert.notNull(taskScheduler, "TaskScheduler must not be null");
this.taskScheduler = taskScheduler;
}
public void setScheduler(@Nullable Object scheduler) {
if (scheduler == null) {
this.taskScheduler = null;
}
else if (scheduler instanceof TaskScheduler) {
this.taskScheduler = (TaskScheduler) scheduler;
}
else if (scheduler instanceof ScheduledExecutorService) {
this.taskScheduler = new ConcurrentTaskScheduler(((ScheduledExecutorService) scheduler));
}
else {
throw new IllegalArgumentException("Unsupported scheduler type: " + scheduler.getClass());
}
}private <T> T resolveSchedulerBean(BeanFactory beanFactory, Class<T> schedulerType, boolean byName) {
if (byName) {
//taskScheduler
T scheduler = beanFactory.getBean(DEFAULT_TASK_SCHEDULER_BEAN_NAME, schedulerType);
if (this.beanName != null && this.beanFactory instanceof ConfigurableBeanFactory) {
((ConfigurableBeanFactory) this.beanFactory).registerDependentBean(
DEFAULT_TASK_SCHEDULER_BEAN_NAME, this.beanName);
}
return scheduler;
}
else if (beanFactory instanceof AutowireCapableBeanFactory) {
NamedBeanHolder<T> holder = ((AutowireCapableBeanFactory) beanFactory).resolveNamedBean(schedulerType);
if (this.beanName != null && beanFactory instanceof ConfigurableBeanFactory) {
((ConfigurableBeanFactory) beanFactory).registerDependentBean(holder.getBeanName(), this.beanName);
}
return holder.getBeanInstance();
}
else {
return beanFactory.getBean(schedulerType);
}
}来源：https://blog.csdn.net/shenchaohao12321/article/details/85857546