前言
當(dāng)一個方法被加上@Schedule注解，然后做一些相關(guān)配置，在Spring容器啟動之后，這個方法就會按照@Schedule注解的配置周期性或者延遲執(zhí)行。Spring是如何辦到這個的，本文就講解一下這塊的原理。
源碼分析
掃描Task
熟悉Spring的人都知道BeanPostProcessor這個回調(diào)接口，Spring框架掃描所有被@Scheduled注解的方法就是通過實(shí)現(xiàn)這個回調(diào)接口來實(shí)現(xiàn)的。
具體實(shí)現(xiàn)類為ScheduledAnnotationBeanPostProcessor，在ScheduledAnnotationBeanPostProcessor的postProcessAfterInitialization會從bean中解析出有@Scheduled注解的方法，然后調(diào)用processScheduled處理這些方法。
public Object postProcessAfterInitialization(final Object bean, String beanName) {
Class<?> targetClass = AopUtils.getTargetClass(bean);
if (!this.nonAnnotatedClasses.contains(targetClass)) {
//掃描bean內(nèi)帶有Scheduled注解的方法
Map<Method, Set<Scheduled>> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
new MethodIntrospector.MetadataLookup<Set<Scheduled>>() {
@Override
public Set<Scheduled> inspect(Method method) {
Set<Scheduled> scheduledMethods =
AnnotatedElementUtils.getMergedRepeatableAnnotations(method, Scheduled.class, Schedules.class);
return (!scheduledMethods.isEmpty() ? scheduledMethods : null);
}
});
if (annotatedMethods.isEmpty()) {
//如果這個class沒有注解的方法，緩存下來，因?yàn)橐粋€class可能有多個bean
this.nonAnnotatedClasses.add(targetClass);
if (logger.isTraceEnabled()) {
logger.trace("No @Scheduled annotations found on bean class: " + bean.getClass());
}
}
else {
// Non-empty set of methods
for (Map.Entry<Method, Set<Scheduled>> entry : annotatedMethods.entrySet()) {
Method method = entry.getKey();
for (Scheduled scheduled : entry.getValue()) {
//處理這些有Scheduled的方法
processScheduled(scheduled, method, bean);
}
}
if (logger.isDebugEnabled()) {
logger.debug(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
"': " + annotatedMethods);
}
}
}
return bean;
}
注冊Task
processScheduled方法會處理這個方法以及它對應(yīng)的注解生成Task，然后把這些Task注冊到ScheduledTaskRegistrar，ScheduledTaskRegistrar負(fù)責(zé)Task的生命周期。
protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
try {
Assert.isTrue(method.getParameterTypes().length == 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<ScheduledTask>(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);
}
try {
initialDelay = Long.parseLong(initialDelayString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid initialDelayString value \"" + initialDelayString + "\" - cannot parse into integer");
}
}
// Check cron expression
String cron = scheduled.cron();
if (StringUtils.hasText(cron)) {
Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
processedSchedule = true;
String zone = scheduled.zone();
if (this.embeddedValueResolver != null) {
cron = this.embeddedValueResolver.resolveStringValue(cron);
zone = this.embeddedValueResolver.resolveStringValue(zone);
}
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 IntervalTask(runnable, fixedDelay, initialDelay)));
}
String fixedDelayString = scheduled.fixedDelayString();
if (StringUtils.hasText(fixedDelayString)) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
if (this.embeddedValueResolver != null) {
fixedDelayString = this.embeddedValueResolver.resolveStringValue(fixedDelayString);
}
try {
fixedDelay = Long.parseLong(fixedDelayString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid fixedDelayString value \"" + fixedDelayString + "\" - cannot parse into integer");
}
tasks.add(this.registrar.scheduleFixedDelayTask(new IntervalTask(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 IntervalTask(runnable, fixedRate, initialDelay)));
}
String fixedRateString = scheduled.fixedRateString();
if (StringUtils.hasText(fixedRateString)) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
if (this.embeddedValueResolver != null) {
fixedRateString = this.embeddedValueResolver.resolveStringValue(fixedRateString);
}
try {
fixedRate = Long.parseLong(fixedRateString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid fixedRateString value \"" + fixedRateString + "\" - cannot parse into integer");
}
tasks.add(this.registrar.scheduleFixedRateTask(new IntervalTask(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<ScheduledTask>(4);
this.scheduledTasks.put(bean, registeredTasks);
}
registeredTasks.addAll(tasks);
}
}
catch (IllegalArgumentException ex) {
throw new IllegalStateException(
"Encountered invalid @Scheduled method '" + method.getName() + "': " + ex.getMessage());
}
}
運(yùn)行Task
任務(wù)注冊到ScheduledTaskRegistrar之后，我們就要運(yùn)行它們。觸發(fā)操作會在下面2個回調(diào)方法內(nèi)觸發(fā)。
afterSingletonsInstantiated和名字一樣，會等所有Singleton類型的bean實(shí)例化后觸發(fā)。
onApplicationEvent會等ApplicationContext完成refresh后被觸發(fā)。
@Override
public void afterSingletonsInstantiated() {
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();
}
}
在finishRegistration中先會對ScheduledTaskRegistrar進(jìn)行初始化，ScheduledTaskRegistrar設(shè)置我們?nèi)萜髦械木€程池，如果沒有配置這個默認(rèn)線程池，ScheduledTaskRegistrar內(nèi)部也會創(chuàng)建一個。初始化完成之后，調(diào)用ScheduledTaskRegistrar的afterPropertiesSet方法運(yùn)行注冊的任務(wù)。
private void finishRegistration() {
if (this.scheduler != null) {
this.registrar.setScheduler(this.scheduler);
}
if (this.beanFactory instanceof ListableBeanFactory) {
Map<String, SchedulingConfigurer> configurers =
((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);
for (SchedulingConfigurer configurer : configurers.values()) {
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(this.beanFactory.getBean(TaskScheduler.class));
}
catch (NoUniqueBeanDefinitionException ex) {
try {
this.registrar.setTaskScheduler(
this.beanFactory.getBean(DEFAULT_TASK_SCHEDULER_BEAN_NAME, TaskScheduler.class));
}
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(this.beanFactory.getBean(ScheduledExecutorService.class));
}
catch (NoUniqueBeanDefinitionException ex2) {
try {
this.registrar.setScheduler(
this.beanFactory.getBean(DEFAULT_TASK_SCHEDULER_BEAN_NAME, ScheduledExecutorService.class));
}
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();
}
ScheduledTaskRegistrar
ScheduledTaskRegistrar內(nèi)部維護(hù)一個線程池以及我們添加的任務(wù)，負(fù)責(zé)任務(wù)的啟動以及停止工作。
private TaskScheduler taskScheduler;
private ScheduledExecutorService localExecutor;
private List<TriggerTask> triggerTasks;
private List<CronTask> cronTasks;
private List<IntervalTask> fixedRateTasks;
private List<IntervalTask> fixedDelayTasks;
private final Map<Task, ScheduledTask> unresolvedTasks = new HashMap<Task, ScheduledTask>(16);
private final Set<ScheduledTask> scheduledTasks = new LinkedHashSet<ScheduledTask>(16);
Task注冊
任務(wù)注冊通過對應(yīng)的add方法，隨便舉個例子如下
public void addFixedRateTask(IntervalTask task) {
if (this.fixedRateTasks == null) {
this.fixedRateTasks = new ArrayList<IntervalTask>();
}
this.fixedRateTasks.add(task);
}
Task執(zhí)行
在ScheduledAnnotationBeanPostProcessor中我們通過ScheduledTaskRegistrar的afterPropertiesSet啟動任務(wù)的執(zhí)行。
public void afterPropertiesSet() {
scheduleTasks();
}
afterPropertiesSet內(nèi)調(diào)用了scheduleTasks方法
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));
}
}
}
在scheduleTasks方法內(nèi)，會通過每種任務(wù)的schedule方法執(zhí)行任務(wù)，schedule方法會返回一個ScheduledTask對象，ScheduledTask主要用來保存任務(wù)的Future，這個Future主要是用來取消任務(wù)執(zhí)行。然后addScheduledTask把ScheduledTask保存起來。
隨便舉一個任務(wù)的schedule方法的例子
public ScheduledTask scheduleFixedDelayTask(IntervalTask task) {
ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
boolean newTask = false;
if (scheduledTask == null) {
scheduledTask = new ScheduledTask();
newTask = true;
}
if (this.taskScheduler != null) {
if (task.getInitialDelay() > 0) {
Date startTime = new Date(System.currentTimeMillis() + task.getInitialDelay());
scheduledTask.future =
this.taskScheduler.scheduleWithFixedDelay(task.getRunnable(), startTime, task.getInterval());
}
else {
scheduledTask.future =
this.taskScheduler.scheduleWithFixedDelay(task.getRunnable(), task.getInterval());
}
}
else {
addFixedDelayTask(task);
this.unresolvedTasks.put(task, scheduledTask);
}
return (newTask ? scheduledTask : null);
}
Task銷毀
ScheduledTaskRegistrar實(shí)現(xiàn)了DisposableBean接口，在這個bean被銷毀的時候，會觸發(fā)取消任務(wù)執(zhí)行。
public void destroy() {
for (ScheduledTask task : this.scheduledTasks) {
task.cancel();
}
if (this.localExecutor != null) {
this.localExecutor.shutdownNow();
}
}
上面調(diào)用了ScheduledTask的cancel方法取消任務(wù)，我們來看下它的實(shí)現(xiàn)。
public final class ScheduledTask {
volatile ScheduledFuture<?> future;
ScheduledTask() {
}
/**
* Trigger cancellation of this scheduled task.
*/
public void cancel() {
ScheduledFuture<?> future = this.future;
if (future != null) {
future.cancel(true);
}
}
}
通過保存任務(wù)的future來對任務(wù)進(jìn)行取消。
