通過前文我們基本梳理了定時任務體系：Timer和ScheduledExecutorService是JDK內置的定時任務方案，以及Netty內部基於時間輪實現的HashedWheelTimer，再到Quartz以及分佈式任務（ElasticJob，xxl-job等等）。對於Springboot簡單應用，還可以採用Spring自帶task方式，本文主要介紹Spring自帶的Task的案例和其實現方式。@pdai
實現案例
Spring Task封裝的比較好，使用非常簡單。
@EnableScheduling+@Scheduled
- 通過@EnableScheduling啓用定時任務，@Scheduled定義任務
@EnableScheduling
@Configuration
public class ScheduleDemo {
/**
* 每隔1分鐘執行一次。
*/
@Scheduled(fixedRate = 1000 * 60 * 1)
public void runScheduleFixedRate() {
log.info("runScheduleFixedRate: current DateTime, {}", LocalDateTime.now());
}
/**
* 每個整點小時執行一次。
*/
@Scheduled(cron = "0 0 */1 * * ?")
public void runScheduleCron() {
log.info("runScheduleCron: current DateTime, {}", LocalDateTime.now());
}
}
- @Scheduled所支持的參數：
cron：cron表達式，指定任務在特定時間執行；fixedDelay：表示上一次任務執行完成後多久再次執行，參數類型爲long，單位ms；fixedDelayString：與fixedDelay含義一樣，只是參數類型變爲String；fixedRate：表示按一定的頻率執行任務，參數類型爲long，單位ms；fixedRateString: 與fixedRate的含義一樣，只是將參數類型變爲String；initialDelay：表示延遲多久再第一次執行任務，參數類型爲long，單位ms；initialDelayString：與initialDelay的含義一樣，只是將參數類型變爲String；zone：時區，默認爲當前時區，一般沒有用到。
進一步理解
我們再通過一些問題來幫助你更深入理解Spring Task實現方式。@pdai
使用Spring Task要注意什麼？
- 關於異常處理
建議自行處理異常
- 關於超時處理
在實際的開發中，這個問題經常會出現，比如執行一段時間後定時任務不再執行了； 這種情況會發生在，比如你調用一個第三方接口，沒有設置調用超時，繼而引發異常，這時候當前任務便阻塞了。
Spring Task的原理？
Spring Task的源碼在這裏：
@EnableScheduling註解
添加@EnableScheduling註解會自動注入SchedulingConfiguration
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.1
* @see Scheduled
* @see SchedulingConfiguration
* @see SchedulingConfigurer
* @see ScheduledTaskRegistrar
* @see Trigger
* @see ScheduledAnnotationBeanPostProcessor
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {
}
SchedulingConfiguration中初始化ScheduledAnnotationBeanPostProcessor
SchedulingConfiguration配置中自動初始化ScheduledAnnotationBeanPostProcessor
@Configuration(proxyBeanMethods = false)
@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();
}
}
什麼是BeanPostProcessor? 我們在前文中有詳解的講解，具體看Spring核心之控制反轉(IOC)源碼解析
Spring 容器中 Bean 的生命週期流程
ScheduledTaskRegistrar註冊task
在ScheduledAnnotationBeanPostProcessor構造函數中初始化了ScheduledTaskRegistrar
/**
* Create a default {@code ScheduledAnnotationBeanPostProcessor}.
*/
public ScheduledAnnotationBeanPostProcessor() {
this.registrar = new ScheduledTaskRegistrar();
}
ScheduledTaskRegistrar最主要的是註冊各種類型的task （這種方式在新的版本中已經廢棄了）
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));
}
}
}
註冊哪些Task，怎麼設計類的呢？
ScheduledAnnotationBeanPostProcessor加載Scheduled註解
在BeanPostProcessor的postProcessAfterInitialization階段加載Scheduled註解
@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> scheduledAnnotations = AnnotatedElementUtils.getMergedRepeatableAnnotations(
method, Scheduled.class, Schedules.class);
return (!scheduledAnnotations.isEmpty() ? scheduledAnnotations : 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, scheduledAnnotations) ->
scheduledAnnotations.forEach(scheduled -> processScheduled(scheduled, method, bean)));
if (logger.isTraceEnabled()) {
logger.trace(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
"': " + annotatedMethods);
}
}
}
return bean;
}
Scheduled註解是添加到方法級別，具體如下
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
/**
* A special cron expression value that indicates a disabled trigger: {@value}.
* <p>This is primarily meant for use with <code>${...}</code> placeholders,
* allowing for external disabling of corresponding scheduled methods.
* @since 5.1
* @see ScheduledTaskRegistrar#CRON_DISABLED
*/
String CRON_DISABLED = ScheduledTaskRegistrar.CRON_DISABLED;
/**
* A cron-like expression, extending the usual UN*X definition to include triggers
* on the second, minute, hour, day of month, month, and day of week.
* <p>For example, {@code "0 * * * * MON-FRI"} means once per minute on weekdays
* (at the top of the minute - the 0th second).
* <p>The fields read from left to right are interpreted as follows.
* <ul>
* <li>second</li>
* <li>minute</li>
* <li>hour</li>
* <li>day of month</li>
* <li>month</li>
* <li>day of week</li>
* </ul>
* <p>The special value {@link #CRON_DISABLED "-"} indicates a disabled cron
* trigger, primarily meant for externally specified values resolved by a
* <code>${...}</code> placeholder.
* @return an expression that can be parsed to a cron schedule
* @see org.springframework.scheduling.support.CronExpression#parse(String)
*/
String cron() default "";
/**
* A time zone for which the cron expression will be resolved. By default, this
* attribute is the empty String (i.e. the server's local time zone will be used).
* @return a zone id accepted by {@link java.util.TimeZone#getTimeZone(String)},
* or an empty String to indicate the server's default time zone
* @since 4.0
* @see org.springframework.scheduling.support.CronTrigger#CronTrigger(String, java.util.TimeZone)
* @see java.util.TimeZone
*/
String zone() default "";
/**
* Execute the annotated method with a fixed period between the end of the
* last invocation and the start of the next.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the delay
*/
long fixedDelay() default -1;
/**
* Execute the annotated method with a fixed period between the end of the
* last invocation and the start of the next.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the delay as a String value — for example, a placeholder
* or a {@link java.time.Duration#parse java.time.Duration} compliant value
* @since 3.2.2
*/
String fixedDelayString() default "";
/**
* Execute the annotated method with a fixed period between invocations.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the period
*/
long fixedRate() default -1;
/**
* Execute the annotated method with a fixed period between invocations.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the period as a String value — for example, a placeholder
* or a {@link java.time.Duration#parse java.time.Duration} compliant value
* @since 3.2.2
*/
String fixedRateString() default "";
/**
* Number of units of time to delay before the first execution of a
* {@link #fixedRate} or {@link #fixedDelay} task.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the initial
* @since 3.2
*/
long initialDelay() default -1;
/**
* Number of units of time to delay before the first execution of a
* {@link #fixedRate} or {@link #fixedDelay} task.
* <p>The time unit is milliseconds by default but can be overridden via
* {@link #timeUnit}.
* @return the initial delay as a String value — for example, a placeholder
* or a {@link java.time.Duration#parse java.time.Duration} compliant value
* @since 3.2.2
*/
String initialDelayString() default "";
/**
* The {@link TimeUnit} to use for {@link #fixedDelay}, {@link #fixedDelayString},
* {@link #fixedRate}, {@link #fixedRateString}, {@link #initialDelay}, and
* {@link #initialDelayString}.
* <p>Defaults to {@link TimeUnit#MICROSECONDS}.
* <p>This attribute is ignored for {@linkplain #cron() cron expressions}
* and for {@link java.time.Duration} values supplied via {@link #fixedDelayString},
* {@link #fixedRateString}, or {@link #initialDelayString}.
* @return the {@code TimeUnit} to use
* @since 5.3.10
*/
TimeUnit timeUnit() default TimeUnit.MILLISECONDS;
}
@Scheduled所支持的參數：
cron：cron表達式，指定任務在特定時間執行；fixedDelay：表示上一次任務執行完成後多久再次執行，參數類型爲long，單位ms；fixedDelayString：與fixedDelay含義一樣，只是參數類型變爲String；fixedRate：表示按一定的頻率執行任務，參數類型爲long，單位ms；fixedRateString: 與fixedRate的含義一樣，只是將參數類型變爲String；initialDelay：表示延遲多久再第一次執行任務，參數類型爲long，單位ms；initialDelayString：與initialDelay的含義一樣，只是將參數類型變爲String；zone：時區，默認爲當前時區，一般沒有用到。
獲取到方法上Scheduled註解（對任務的定義），通過processScheduled處理具體類型的task
/**
* Process the given {@code @Scheduled} method declaration on the given bean.
* @param scheduled the {@code @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 = convertToMillis(scheduled.initialDelay(), scheduled.timeUnit());
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 = convertToMillis(initialDelayString, scheduled.timeUnit());
}
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 = convertToMillis(scheduled.fixedDelay(), scheduled.timeUnit());
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 = convertToMillis(fixedDelayString, scheduled.timeUnit());
}
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 = convertToMillis(scheduled.fixedRate(), scheduled.timeUnit());
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 = convertToMillis(fixedRateString, scheduled.timeUnit());
}
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());
}
}
ScheduledTaskRegistrar 中解析task
以CronTask爲例，如果定義了taskScheduler則由taskScheduler執行，如果沒有放到unresolvedTasks中。
/**
* Schedule the specified cron task, either right away if possible
* or on initialization of the scheduler.
* @return a handle to the scheduled task, allowing to cancel it
* (or {@code null} if processing a previously registered task)
* @since 4.3
*/
@Nullable
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對Task處理
默認是ConcurrentTaskScheduler， 處理方法如下
@Override
@Nullable
public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
try {
if (this.enterpriseConcurrentScheduler) {
return new EnterpriseConcurrentTriggerScheduler().schedule(decorateTask(task, true), trigger);
}
else {
ErrorHandler errorHandler =
(this.errorHandler != null ? this.errorHandler : TaskUtils.getDefaultErrorHandler(true));
return new ReschedulingRunnable(task, trigger, this.clock, this.scheduledExecutor, errorHandler).schedule();
}
}
catch (RejectedExecutionException ex) {
throw new TaskRejectedException("Executor [" + this.scheduledExecutor + "] did not accept task: " + task, ex);
}
}
EnterpriseConcurrentTriggerScheduler 是 JSR-236 Trigger標準，它的處理方法如下
/**
* Delegate that adapts a Spring Trigger to a JSR-236 Trigger.
* Separated into an inner class in order to avoid a hard dependency on the JSR-236 API.
*/
private class EnterpriseConcurrentTriggerScheduler {
public ScheduledFuture<?> schedule(Runnable task, final Trigger trigger) {
ManagedScheduledExecutorService executor = (ManagedScheduledExecutorService) scheduledExecutor;
return executor.schedule(task, new javax.enterprise.concurrent.Trigger() {
@Override
@Nullable
public Date getNextRunTime(@Nullable LastExecution le, Date taskScheduledTime) {
return (trigger.nextExecutionTime(le != null ?
new SimpleTriggerContext(le.getScheduledStart(), le.getRunStart(), le.getRunEnd()) :
new SimpleTriggerContext()));
}
@Override
public boolean skipRun(LastExecution lastExecution, Date scheduledRunTime) {
return false;
}
});
}
}
如果沒有使用EnterpriseConcurrentTriggerScheduler, 則使用ReschedulingRunnable，本質上由ScheduledExecutorService處理
public ReschedulingRunnable(Runnable delegate, Trigger trigger, Clock clock,
ScheduledExecutorService executor, ErrorHandler errorHandler) {
super(delegate, errorHandler);
this.trigger = trigger;
this.triggerContext = new SimpleTriggerContext(clock);
this.executor = executor;
}
@Nullable
public ScheduledFuture<?> schedule() {
synchronized (this.triggerContextMonitor) {
this.scheduledExecutionTime = this.trigger.nextExecutionTime(this.triggerContext);
if (this.scheduledExecutionTime == null) {
return null;
}
long initialDelay = this.scheduledExecutionTime.getTime() - this.triggerContext.getClock().millis();
this.currentFuture = this.executor.schedule(this, initialDelay, TimeUnit.MILLISECONDS);
return this;
}
}
示例源碼
https://github.com/realpdai/tech-pdai-spring-demos
更多內容
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