1. Examples
It is very simple to use a timer in SpringBoot. First, define a class that needs to be executed regularly, then define a method that needs to be executed, and add the @Scheduled annotation to the method
@Component
public class ScheduleTest {
@Scheduled(cron = "*/4 * * * * *")
public void scheduleCheck2(){
System.out.println("task2 begin: "+new Date());
try {
Thread.sleep(3000l);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("task2 end : "+new Date());
}
}Then add the @EnableScheduling annotation to the startup class.
Execution effect:
2. Source code analysis
First look at the @EnableScheduling annotation, which imports the SchedulingConfiguration class.
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {
}The SchedulingConfiguration class creates a ScheduledAnnotationBeanPostProcessor object.
@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();
}
}The ScheduledAnnotationBeanPostProcessor object implements the BeanPostProcessor and ApplicationListener interfaces, in the postProcessAfterInitialization method of ScheduledAnnotationBeanPostProcessor
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)) {
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;
}It can be seen that the logic is very simple, that is, to find all Bean methods with @Scheduled annotation on the method, and then execute the processScheduled 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());
}
}The logic of this method is also very simple, steps:
1. First parse the delayed execution time for the first time, and then parse the cron timing execution time
2. If cron timing is configured, add a timing task and set processedSchedule to true. It will not be added later even if fixed frequency and delayed execution are configured.
3. If no cron task is set, it is judged whether to set the delay time after each task execution is completed before executing the task. That is, the fixedDelay parameter task.
4. If the delayed task is not set, then judge whether there is a fixed frequency task. That is, the fixedRate parameter task.
After the postProcessAfterInitialization method is executed, and after the Bean is created, Spring will notify the event through the Refresh method and execute the onApplicationEvent method after loading.
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.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));
}
......................
this.registrar.afterPropertiesSet();
}A timed thread pool will be set, which can be set manually. SpringBoot will automatically inject a default thread pool through TaskSchedulingAutoConfiguration when loading, coreSize =1, so if we have multiple Scheduled tasks, they will be serialized one by one Waits for the task to complete before executing it. Concurrency can be improved by modifying the coreSize of the default thread pool. The parameter is: spring.task.scheduling.pool.size = XX.
Then execute the this.registrar.afterPropertiesSet() method.
public void afterPropertiesSet() {
scheduleTasks();
}
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));
}
}
}Let's take cronTasks as an example.
public ScheduledTask scheduleCronTask(CronTask task) {
ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
boolean newTask = false;
if (scheduledTask == null) {
scheduledTask = new ScheduledTask(task);
newTask = true;
}
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);
}taskScheduler.schedule(task.getRunnable(), task.getTrigger())方法
public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
ScheduledExecutorService executor = getScheduledExecutor();
try {
ErrorHandler errorHandler = this.errorHandler;
if (errorHandler == null) {
errorHandler = TaskUtils.getDefaultErrorHandler(true);
}
return new ReschedulingRunnable(task, trigger, executor, errorHandler).schedule();
}
catch (RejectedExecutionException ex) {
throw new TaskRejectedException("Executor [" + executor + "] did not accept task: " + task, ex);
}
}Created a ReschedulingRunnable that is re-executable Runnable.
public ReschedulingRunnable(
Runnable delegate, Trigger trigger, ScheduledExecutorService executor, ErrorHandler errorHandler) {
super(delegate, errorHandler);
this.trigger = trigger;
this.executor = executor;
}
public void run() {
Date actualExecutionTime = new Date();
super.run();
Date completionTime = new Date();
synchronized (this.triggerContextMonitor) {
Assert.state(this.scheduledExecutionTime != null, "No scheduled execution");
this.triggerContext.update(this.scheduledExecutionTime, actualExecutionTime, completionTime);
if (!obtainCurrentFuture().isCancelled()) {
schedule();
}
}
}After executing the run method, it will continue to call its own schedule method.
public ScheduledFuture<?> schedule() {
synchronized (this.triggerContextMonitor) {
this.scheduledExecutionTime = this.trigger.nextExecutionTime(this.triggerContext);
if (this.scheduledExecutionTime == null) {
return null;
}
long initialDelay = this.scheduledExecutionTime.getTime() - System.currentTimeMillis();
this.currentFuture = this.executor.schedule(this, initialDelay, TimeUnit.MILLISECONDS);
return this;
}
}The schedule method will put itself into the scheduling thread pool to continue execution, and this reciprocation forms a regular execution.
Simply put, it uses the ScheduledThreadPoolExecutor that comes with java to schedule the thread pool for timing.