1、Spring中的定时任务
1.1、使用xml形式
任务类MyScheduler:
public class MyScheduler {
public void print(){
System.out.println("MyScheduler：" + LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS")));
}
}
spring配置spring-task.xml:
<task:annotation-driven/>
<bean id="taskScheduler" class="org.com.cay.scheduler.MyScheduler"/>
<task:scheduled-tasks>
<task:scheduled ref="taskScheduler" method="print" cron="0/5 * * * * ?"/>
</task:scheduled-tasks>
运行项目即可实现每隔5s会输出一次信息。
1.2、使用注解形式
@Component
public class OtherScheduler {
@Scheduled(cron="0/10 * * * * ?")
public void show(){
System.out.println("OtherScheduler：" + LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS")));
}
}
运行项目即可实现每隔10s会输出一次信息。
2、task命名空间
task命名空间使用 TaskNamespaceHandler 来处理:
//{@code NamespaceHandler} for the 'task' namespace.
public class TaskNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
this.registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
this.registerBeanDefinitionParser("executor", new ExecutorBeanDefinitionParser());
this.registerBeanDefinitionParser("scheduled-tasks", new ScheduledTasksBeanDefinitionParser());
this.registerBeanDefinitionParser("scheduler", new SchedulerBeanDefinitionParser());
}
}
而其中：
-
AnnotationDrivenBeanDefinitionParser用于解析<task:annotation-driven />标签：
<task:annotation-driven scheduler="" exception-handler="" executor="" mode="" proxy-target-class=""/>
-
SchedulerBeanDefinitionParser用于解析<task:scheduler />标签:
<task:scheduler id="调度器id" pool-size="线程池大小" />
-
ScheduledTasksBeanDefinitionParser用于解析<task:scheduled-tasks />标签:
<task:scheduled-tasks scheduler="指定使用调度器的id"> <task:scheduled ref="任务bean" method="任务bean的方法" cron="" fixed-delay="" fixed-rate="" initial-delay="" trigger=""/> </task:scheduled-tasks>
-
ExecutorBeanDefinitionParser用于解析<task:executor />标签:
<task:executor id="" pool-size="" keep-alive="" queue-capacity="" rejection-policy="" />
3、源码分析
3.1、SchedulerBeanDefinitionParser：
直接看类定义：
public class SchedulerBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
@Override
protected String getBeanClassName(Element element) {
return "org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler";
}
@Override
protected void doParse(Element element, BeanDefinitionBuilder builder) {
String poolSize = element.getAttribute("pool-size");
if (StringUtils.hasText(poolSize)) {
builder.addPropertyValue("poolSize", poolSize);
}
}
}
可以想象，一旦配置了
<task:scheduler id="调度器id" pool-size="线程池大小" />
，就会向Spring容器中注册一个Bean，id为指定的id值，值为org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler类的实例。
至于我为什么会先讲这个类，后面会解释。
3.2、ExecutorBeanDefinitionParser：
直接看类定义：
public class ExecutorBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
@Override
protected String getBeanClassName(Element element) {
return "org.springframework.scheduling.config.TaskExecutorFactoryBean";
}
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
String keepAliveSeconds = element.getAttribute("keep-alive");
if (StringUtils.hasText(keepAliveSeconds)) {
builder.addPropertyValue("keepAliveSeconds", keepAliveSeconds);
}
String queueCapacity = element.getAttribute("queue-capacity");
if (StringUtils.hasText(queueCapacity)) {
builder.addPropertyValue("queueCapacity", queueCapacity);
}
configureRejectionPolicy(element, builder);
String poolSize = element.getAttribute("pool-size");
if (StringUtils.hasText(poolSize)) {
builder.addPropertyValue("poolSize", poolSize);
}
}
//configureRejectionPolicy函数...
}
同上节一样，一旦配置了
<task:executor id="" pool-size="" keep-alive="" queue-capacity="" rejection-policy="" />
，就会向Spring容器中注册一个Bean，值为org.springframework.scheduling.config.TaskExecutorFactoryBean类的实例对象。
3.3、AnnotationDrivenBeanDefinitionParser：
该类用于解析使用注解形式的任务调度，看源码（部分）：
public class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
private static final String ASYNC_EXECUTION_ASPECT_CLASS_NAME =
"org.springframework.scheduling.aspectj.AnnotationAsyncExecutionAspect";
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
Object source = parserContext.extractSource(element);
// Register component for the surrounding <task:annotation-driven> element.
CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
parserContext.pushContainingComponent(compDefinition);
// Nest the concrete post-processor bean in the surrounding component.
BeanDefinitionRegistry registry = parserContext.getRegistry();
String mode = element.getAttribute("mode");
if ("aspectj".equals(mode)) {
// mode="aspectj"
registerAsyncExecutionAspect(element, parserContext);
}
else {
// mode="proxy"
if (registry.containsBeanDefinition(TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME)) {
parserContext.getReaderContext().error(
"Only one AsyncAnnotationBeanPostProcessor may exist within the context.", source);
}
else {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(
"org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor");
builder.getRawBeanDefinition().setSource(source);
String executor = element.getAttribute("executor");
if (StringUtils.hasText(executor)) {
builder.addPropertyReference("executor", executor);
}
String exceptionHandler = element.getAttribute("exception-handler");
if (StringUtils.hasText(exceptionHandler)) {
builder.addPropertyReference("exceptionHandler", exceptionHandler);
}
if (Boolean.valueOf(element.getAttribute(AopNamespaceUtils.PROXY_TARGET_CLASS_ATTRIBUTE))) {
builder.addPropertyValue("proxyTargetClass", true);
}
registerPostProcessor(parserContext, builder, TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME);
}
}
if (registry.containsBeanDefinition(TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
parserContext.getReaderContext().error(
"Only one ScheduledAnnotationBeanPostProcessor may exist within the context.", source);
}
else {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(
"org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor");
builder.getRawBeanDefinition().setSource(source);
String scheduler = element.getAttribute("scheduler");
if (StringUtils.hasText(scheduler)) {
builder.addPropertyReference("scheduler", scheduler);
}
registerPostProcessor(parserContext, builder, TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME);
}
// Finally register the composite component.
parserContext.popAndRegisterContainingComponent();
return null;
}
//other code...
}
从AnnotationDrivenBeanDefinitionParserd源码中可以看到，它注册了两个后置处理器，分别是：
-
org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor
-
org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor
前者用于异步调用的处理器，而后者用于任务调度的处理器。
本文主要讲解任务调度，所以来看ScheduledAnnotationBeanPostProcessor处理器。
首先来看看ScheduledAnnotationBeanPostProcessor类定义：
public class ScheduledAnnotationBeanPostProcessor
implements MergedBeanDefinitionPostProcessor, DestructionAwareBeanPostProcessor,
Ordered, EmbeddedValueResolverAware, BeanNameAware, BeanFactoryAware, ApplicationContextAware,
SmartInitializingSingleton, ApplicationListener<ContextRefreshedEvent>, DisposableBean {}
从类定义来看，ScheduledAnnotationBeanPostProcessor实现了ApplicationListener接口，用于监听ContextRefreshedEvent事件。
先来看初始化后的后置处理方法ScheduledAnnotationBeanPostProcessor#postProcessAfterInitialization方法：
@Override
public Object postProcessAfterInitialization(final Object bean, String beanName) {
Class<?> targetClass = AopUtils.getTargetClass(bean);
if (!this.nonAnnotatedClasses.contains(targetClass)) {
//首先获取所有带有注解（@Scheduled和@Schedules）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);
}
});
//如果注解方法集合为空
if (annotatedMethods.isEmpty()) {
this.nonAnnotatedClasses.add(targetClass);
if (logger.isTraceEnabled()) {
logger.trace("No @Scheduled annotations found on bean class: " + bean.getClass());
}
}
else {
//带有注解的方法集合不为空时
for (Map.Entry<Method, Set<Scheduled>> entry : annotatedMethods.entrySet()) {
Method method = entry.getKey();
for (Scheduled scheduled : entry.getValue()) {
//依次遍历处理注解方法，重点
processScheduled(scheduled, method, bean);
}
}
if (logger.isDebugEnabled()) {
logger.debug(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
"': " + annotatedMethods);
}
}
}
return bean;
}
再来看处理定时任务的方法ScheduledAnnotationBeanPostProcessor#processScheduled方法：
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());
//创建ScheduledMethodRunnable(父接口Runnable)对象，主要是用来反射定时方法
Runnable runnable = new ScheduledMethodRunnable(bean, invocableMethod);
boolean processedSchedule = false;
String errorMessage =
"Exactly one of the 'cron', 'fixedDelay(String)', or 'fixedRate(String)' attributes is required";
// 初始化一个定时任务集合
Set<ScheduledTask> tasks = new LinkedHashSet<ScheduledTask>(4);
// Determine initial delay
//判断注解属性中是否带有initialDelay和initialDelayString
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
//判断是否是cron表达式
String cron = scheduled.cron();
if (StringUtils.hasText(cron)) {
Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
processedSchedule = true;
//获取注解属性中的zone时区值
String zone = scheduled.zone();
if (this.embeddedValueResolver != null) {
cron = this.embeddedValueResolver.resolveStringValue(cron);
zone = this.embeddedValueResolver.resolveStringValue(zone);
}
TimeZone timeZone;
if (StringUtils.hasText(zone)) {
//解析时区
timeZone = StringUtils.parseTimeZoneString(zone);
}
else {
//创建默认时区
timeZone = TimeZone.getDefault();
}
//将表达式解析成cron任务计划添加到任务集合中
//调用ScheduledTaskRegistrar对象的scheduleCronTask(CronTask cronTask)方法
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
//判断是否有fixedDelay属性
long fixedDelay = scheduled.fixedDelay();
if (fixedDelay >= 0) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
//根据属性值创建Interval任务然后添加到任务集合中
//调用ScheduledTaskRegistrar对象的scheduleFixedDelayTask(IntervalTask task)方法
tasks.add(this.registrar.scheduleFixedDelayTask(new IntervalTask(runnable, fixedDelay, initialDelay)));
}
//判断是否有fixedDelayString属性
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");
}
//根据属性值创建Interval任务然后添加到任务集合中
//调用ScheduledTaskRegistrar对象的scheduleFixedDelayTask(IntervalTask task)方法
tasks.add(this.registrar.scheduleFixedDelayTask(new IntervalTask(runnable, fixedDelay, initialDelay)));
}
// Check fixed rate
//判断是否有fixedRate属性
long fixedRate = scheduled.fixedRate();
if (fixedRate >= 0) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
//根据属性值创建Interval任务然后添加到任务集合中
//调用ScheduledTaskRegistrar对象的scheduleFixedRateTask(IntervalTask task)方法
tasks.add(this.registrar.scheduleFixedRateTask(new IntervalTask(runnable, fixedRate, initialDelay)));
}
//判断是否有fixedRateString属性
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");
}
//根据属性值创建Interval任务然后添加到任务集合中
//调用ScheduledTaskRegistrar对象的scheduleFixedRateTask(IntervalTask task)方法
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());
}
}
上述源码中讲到了ScheduledMethodRunnable类，该类实现了Runnable接口：
public class ScheduledMethodRunnable implements Runnable {
private final Object target;
private final Method method;
//constructor and getter/setter...
@Override
public void run() {
try {
//定时任务的反射机制
ReflectionUtils.makeAccessible(this.method);
this.method.invoke(this.target);
}
catch (InvocationTargetException ex) {
ReflectionUtils.rethrowRuntimeException(ex.getTargetException());
}
catch (IllegalAccessException ex) {
throw new UndeclaredThrowableException(ex);
}
}
}
在processScheduled方法中，对于每种不同属性的情况，会创建不同类型的Task。此处我们以CronTask为例，其余会在后续中提到，接下来咱们来看ScheduledTaskRegistrar#scheduleCronTask方法：
public ScheduledTask scheduleCronTask(CronTask task) {
ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
boolean newTask = false;
if (scheduledTask == null) {
scheduledTask = new ScheduledTask();
newTask = true;
}
//重点
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);
}
因为AnnotationDrivenBeanDefinitionParser是基于注解形式，无法在注解上指定使用的TaskScheduler任务调度器，所以在上述源码中有taskScheduler变量，在Spring启动过程中，父接口ApplicationListener在Spring容器未完全启动之前，即在ContextRefreshedEvent事件未发布之前，该taskScheduler变量仍为null值。
当ContextRefreshedEvent事件发布后，监听到ContextRefreshedEvent事件，则会触发方法：
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
if (event.getApplicationContext() == this.applicationContext) {
//完成注册后
finishRegistration();
}
}
看ScheduledAnnotationBeanPostProcessor#finishRegistration方法:
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<SchedulingConfigurer>(beans.values());
AnnotationAwareOrderComparator.sort(configurers);
for (SchedulingConfigurer configurer : configurers) {
configurer.configureTasks(this.registrar);
}
}
//如果有任务，但是scheduler任务调度器为null时
if (this.registrar.hasTasks() && this.registrar.getScheduler() == null) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to find scheduler by type");
try {
// 开始查找TaskScheduler类型的Bean
this.registrar.setTaskScheduler(resolveSchedulerBean(TaskScheduler.class, false));
}
catch (NoUniqueBeanDefinitionException ex) {
logger.debug("Could not find unique TaskScheduler bean", ex);
try {
//根据名字和类来查找
this.registrar.setTaskScheduler(resolveSchedulerBean(TaskScheduler.class, true));
}
catch (NoSuchBeanDefinitionException ex2) {
//logger
}
}
catch (NoSuchBeanDefinitionException ex) {
logger.debug("Could not find default TaskScheduler bean", ex);
// Search for ScheduledExecutorService bean next...
try {
// 如果没有TaskScheduler类型的Bean，则查找ScheduledExecutorService类型的Bean
this.registrar.setScheduler(resolveSchedulerBean(ScheduledExecutorService.class, false));
}
catch (NoUniqueBeanDefinitionException ex2) {
logger.debug("Could not find unique ScheduledExecutorService bean", ex2);
try {
//根据名字和类来查找
this.registrar.setScheduler(resolveSchedulerBean(ScheduledExecutorService.class, true));
}
catch (NoSuchBeanDefinitionException ex3) {
//logger
}
}
catch (NoSuchBeanDefinitionException ex2) {
//logger
}
}
}
this.registrar.afterPropertiesSet();
}
从上面源码中，会从BeanFactory中试图获取TaskScheduler或ScheduledExecutorService的Bean。
public static final String DEFAULT_TASK_SCHEDULER_BEAN_NAME = "taskScheduler";
private <T> T resolveSchedulerBean(Class<T> schedulerType, boolean byName) {
if (byName) {
//根据name和类来查找
T scheduler = this.beanFactory.getBean(DEFAULT_TASK_SCHEDULER_BEAN_NAME, schedulerType);
if (this.beanFactory instanceof ConfigurableBeanFactory) {
((ConfigurableBeanFactory) this.beanFactory).registerDependentBean(
DEFAULT_TASK_SCHEDULER_BEAN_NAME, this.beanName);
}
return scheduler;
}
//根据类来查找
else if (this.beanFactory instanceof AutowireCapableBeanFactory) {
NamedBeanHolder<T> holder = ((AutowireCapableBeanFactory) this.beanFactory).resolveNamedBean(schedulerType);
if (this.beanFactory instanceof ConfigurableBeanFactory) {
((ConfigurableBeanFactory) this.beanFactory).registerDependentBean(
holder.getBeanName(), this.beanName);
}
return holder.getBeanInstance();
}
else {
return this.beanFactory.getBean(schedulerType);
}
}
这里就要解释下在第3.1、SchedulerBeanDefinitionParser小节留下的疑惑：
- 如果配置了<task:scheduler id="调度器id" pool-size="线程池大小" />，就会注册一个Bean，该Bean的值为org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler类的实例，而这个类又实现了TaskScheduler接口。所以如果配置了，就能从BeanFactory中获取该Bean的值，然后使用ScheduledTaskRegistrar的setTaskScheduler方法设置TaskScheduler对象的值，此时taskScheduler就不再为null了，而是ThreadPoolTaskScheduler类型的任务调度器。
- 如果未配置<task:scheduler id="调度器id" pool-size="线程池大小" />，则无法从BeanFactory中获取对应class或者name的Bean，此时taskScheduler仍为null。
接着看ScheduledTaskRegistrar#afterPropertiesSet和scheduleTasks方法：
@Override
public void afterPropertiesSet() {
scheduleTasks();
}
protected void scheduleTasks() {
//判断taskScheduler是否为null，如果配置了<task:scheduler id="" pool-size=""/>标签，则taskScheduler就不为null了，直接跳过创建调度器的代码
if (this.taskScheduler == null) {
//则创建一个单线程的线程池，和一个ConcurrentTaskScheduler类型的任务调度器
this.localExecutor = Executors.newSingleThreadScheduledExecutor();
this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
}
//将任务添加到任务调度器中进行执行
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));
}
}
}
private void addScheduledTask(ScheduledTask task) {
if (task != null) {
this.scheduledTasks.add(task);
}
}
又回归到了ScheduledTaskRegistrar#scheduleCronTask方法，在进入scheduleTasks方法之后，会先判断taskScheduler是否为null值，如果是null，则创建一个ConcurrentTaskScheduler类型的TaskScheduler；如果不为null(即ThreadPoolTaskScheduler类似)，则跳过创建过程。所以在scheduleCronTask方法中的taskScheduler已经不为null了，所以可以执行调度器scheduler的schedule方法：
public ScheduledTask scheduleCronTask(CronTask task) {
ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
boolean newTask = false;
if (scheduledTask == null) {
scheduledTask = new ScheduledTask();
newTask = true;
}
//此时taskScheduler不为null
if (this.taskScheduler != null) {
//执行TaskScheduler的schedule方法
scheduledTask.future = this.taskScheduler.schedule(task.getRunnable(), task.getTrigger());
}
else {
addCronTask(task);
this.unresolvedTasks.put(task, scheduledTask);
}
return (newTask ? scheduledTask : null);
}
TaskScheduler是个接口，主要有ThreadPoolTaskScheduler和ConcurrentTaskScheduler两个实现类。
看ThreadPoolTaskScheduler#schedule方法：
@Override
public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
ScheduledExecutorService executor = getScheduledExecutor();
try {
ErrorHandler errorHandler =
(this.errorHandler != null ? this.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);
}
}
再看ConcurrentTaskScheduler#schedule方法：
@Override
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));
//调用ReschedulingRunnable对象的schedule方法，触发run方法
return new ReschedulingRunnable(task, trigger, this.scheduledExecutor, errorHandler).schedule();
}
}
catch (RejectedExecutionException ex) {
throw new TaskRejectedException("Executor [" + this.scheduledExecutor + "] did not accept task: " + task, ex);
}
}
其实两者类似，最后都是调用了ReschedulingRunnable类的schedule方法，而schedule方法会触发Runnable接口实现类的run方法的执行，从而导致自定义的任务方法触发执行。
来看看ReschedulingRunnable类的构造函数和执行方法：
class ReschedulingRunnable extends DelegatingErrorHandlingRunnable implements ScheduledFuture<Object> {
//构造函数
public ReschedulingRunnable(Runnable delegate, Trigger trigger, ScheduledExecutorService executor, ErrorHandler errorHandler) {
super(delegate, errorHandler);
this.trigger = trigger;
this.executor = executor;
}
public ScheduledFuture<?> schedule() {
synchronized (this.triggerContextMonitor) {
//计算下一次执行时间
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;
}
}
@Override
public void run() {
Date actualExecutionTime = new Date();
//调用父类的run方法
super.run();
Date completionTime = new Date();
synchronized (this.triggerContextMonitor) {
this.triggerContext.update(this.scheduledExecutionTime, actualExecutionTime, completionTime);
if (!this.currentFuture.isCancelled()) {
// 继续无限调度
schedule();
}
}
}
}
super.run();会调用父类DelegatingErrorHandlingRunnable的run方法，父类run方法中最重要的一句：this.delegate.run();即调用Runnable的run方法，而此时Runnable对象实际上是上述ScheduledMethodRunnable对象，其中封装了自定义的任务方法。最后归根结底，就是通过一层层封装来执行自定义的任务方法。
3.4、ScheduledTasksBeanDefinitionParser
该类用于解析使用xml配置形式的任务调度，看源码（部分）：
public class ScheduledTasksBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
@Override
protected String getBeanClassName(Element element) {
return "org.springframework.scheduling.config.ContextLifecycleScheduledTaskRegistrar";
}
//other code...
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
builder.setLazyInit(false); // lazy scheduled tasks are a contradiction in terms -> force to false
//创建四种集合，分别用来管理四种不同参数或者属性的Task任务
ManagedList<RuntimeBeanReference> cronTaskList = new ManagedList<RuntimeBeanReference>();
ManagedList<RuntimeBeanReference> fixedDelayTaskList = new ManagedList<RuntimeBeanReference>();
ManagedList<RuntimeBeanReference> fixedRateTaskList = new ManagedList<RuntimeBeanReference>();
ManagedList<RuntimeBeanReference> triggerTaskList = new ManagedList<RuntimeBeanReference>();
//解析xml节点
NodeList childNodes = element.getChildNodes();
for (int i = 0; i < childNodes.getLength(); i++) {
Node child = childNodes.item(i);
//判断是否是<task:scheduled />节点
if (!isScheduledElement(child, parserContext)) {
continue;
}
Element taskElement = (Element) child;
//获取节点属性
String ref = taskElement.getAttribute("ref");
String method = taskElement.getAttribute("method");
// Check that 'ref' and 'method' are specified
if (!StringUtils.hasText(ref) || !StringUtils.hasText(method)) {
parserContext.getReaderContext().error("Both 'ref' and 'method' are required", taskElement);
// Continue with the possible next task element
continue;
}
//获取节点属性值
String cronAttribute = taskElement.getAttribute("cron");
String fixedDelayAttribute = taskElement.getAttribute("fixed-delay");
String fixedRateAttribute = taskElement.getAttribute("fixed-rate");
String triggerAttribute = taskElement.getAttribute("trigger");
String initialDelayAttribute = taskElement.getAttribute("initial-delay");
boolean hasCronAttribute = StringUtils.hasText(cronAttribute);
boolean hasFixedDelayAttribute = StringUtils.hasText(fixedDelayAttribute);
boolean hasFixedRateAttribute = StringUtils.hasText(fixedRateAttribute);
boolean hasTriggerAttribute = StringUtils.hasText(triggerAttribute);
boolean hasInitialDelayAttribute = StringUtils.hasText(initialDelayAttribute);
if (!(hasCronAttribute || hasFixedDelayAttribute || hasFixedRateAttribute || hasTriggerAttribute)) {
parserContext.getReaderContext().error(
"one of the 'cron', 'fixed-delay', 'fixed-rate', or 'trigger' attributes is required", taskElement);
continue; // with the possible next task element
}
if (hasInitialDelayAttribute && (hasCronAttribute || hasTriggerAttribute)) {
parserContext.getReaderContext().error(
"the 'initial-delay' attribute may not be used with cron and trigger tasks", taskElement);
continue; // with the possible next task element
}
//创建Runnable对象，并返回该对象的name，见下文#1
String runnableName =
runnableReference(ref, method, taskElement, parserContext).getBeanName();
//以下四种类型的Task，将不同属性和Runnable对象实例绑定对应的Task类上，见下文#2以CronTask为例
if (hasFixedDelayAttribute) {
fixedDelayTaskList.add(intervalTaskReference(runnableName,
initialDelayAttribute, fixedDelayAttribute, taskElement, parserContext));
}
if (hasFixedRateAttribute) {
fixedRateTaskList.add(intervalTaskReference(runnableName,
initialDelayAttribute, fixedRateAttribute, taskElement, parserContext));
}
if (hasCronAttribute) {
cronTaskList.add(cronTaskReference(runnableName, cronAttribute,
taskElement, parserContext));
}
if (hasTriggerAttribute) {
String triggerName = new RuntimeBeanReference(triggerAttribute).getBeanName();
triggerTaskList.add(triggerTaskReference(runnableName, triggerName,
taskElement, parserContext));
}
}
String schedulerRef = element.getAttribute("scheduler");
if (StringUtils.hasText(schedulerRef)) {
//如果有节点上scheduler属性，则进行绑定
builder.addPropertyReference("taskScheduler", schedulerRef);
}
builder.addPropertyValue("cronTasksList", cronTaskList);
builder.addPropertyValue("fixedDelayTasksList", fixedDelayTaskList);
builder.addPropertyValue("fixedRateTasksList", fixedRateTaskList);
builder.addPropertyValue("triggerTasksList", triggerTaskList);
}
//other code...
}
使用ScheduledTasksBeanDefinitionParser解析器，会创建一个类型为org.springframework.scheduling.config.ContextLifecycleScheduledTaskRegistrar的Bean。
doParse源码的#1处
ScheduledTasksBeanDefinitionParser#runnableReference方法：
private RuntimeBeanReference runnableReference(String ref, String method, Element taskElement, ParserContext parserContext) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(
"org.springframework.scheduling.support.ScheduledMethodRunnable");
builder.addConstructorArgReference(ref);
builder.addConstructorArgValue(method);
return beanReference(taskElement, parserContext, builder);
}
再看看ScheduledTasksBeanDefinitionParser#beanReference方法定义：
private RuntimeBeanReference beanReference(Element taskElement,
ParserContext parserContext, BeanDefinitionBuilder builder) {
// Extract the source of the current task
builder.getRawBeanDefinition().setSource(parserContext.extractSource(taskElement));
String generatedName = parserContext.getReaderContext().generateBeanName(builder.getRawBeanDefinition());
parserContext.registerBeanComponent(new BeanComponentDefinition(builder.getBeanDefinition(), generatedName));
return new RuntimeBeanReference(generatedName);
}
上述源码中可以看出，它声明了一个ScheduledMethodRunnable对象的实例，并把任务类和任务的方法绑定到该对象上，并进行注册。
doParse源码的#2处，以CronTask为例：
ScheduledTasksBeanDefinitionParser#cronTaskReference方法：
private RuntimeBeanReference cronTaskReference(String runnableBeanName,
String cronExpression, Element taskElement, ParserContext parserContext) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(
"org.springframework.scheduling.config.CronTask");
builder.addConstructorArgReference(runnableBeanName);
builder.addConstructorArgValue(cronExpression);
return beanReference(taskElement, parserContext, builder);
}
同runnableReference方法一样，在cronTaskReference方法中，同样声明了一个CronTask对象实例，然后将Runnable对象的name以及cron表达式绑定到CronTask对象实例上，并进行注册。
最后将所有的任务加入到不同的任务集合中，并把任务集合绑定到类型为org.springframework.scheduling.config.ContextLifecycleScheduledTaskRegistrar的Bean上。
看看ContextLifecycleScheduledTaskRegistrar的类定义:
public class ContextLifecycleScheduledTaskRegistrar extends ScheduledTaskRegistrar implements SmartInitializingSingleton {
@Override
public void afterPropertiesSet() {
// no-op
}
@Override
public void afterSingletonsInstantiated() {
scheduleTasks();
}
}
在处理ContextLifecycleScheduledTaskRegistrar的Bean的时候，会触发父类的scheduleTasks方法。
此时又回归到了ScheduledTaskRegistrar的scheduleTasks方法了。
ScheduledTaskRegistrar#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ScheduledTasksBeanDefinitionParser的doParse方法中有几行代码：
String schedulerRef = element.getAttribute("scheduler");
if (StringUtils.hasText(schedulerRef)) {
//如果有节点上scheduler属性，则进行绑定
builder.addPropertyReference("taskScheduler", schedulerRef);
}
正如我注释所言：
- 如果节点上指定了scheduler属性，则会把scheduler的引用Bean绑定到ContextLifecycleScheduledTaskRegistrar(ScheduledTaskRegistrar子类)类实例上，则父类ScheduledTaskRegistrar的taskScheduler的值就会赋值为指定的scheduler任务调度器的值，此时的taskScheduler通常为ThreadPoolTaskScheduler类型。
- 如果节点上未指定scheduler属性，即使配置了<task:scheduler id="" pool-size="" />，也不会把当前任务绑定到之前配置的scheduler上去，因为此时taskScheduler为null，它会自己创建一个ConcurrentTaskScheduler类型的TaskScheduler，而不是实际配置的ThreadPoolTaskScheduler类型的TaskScheduler。
最后执行的步骤跟使用注解的方式就一样了，这里就不再累赘了。请参看第3.3小节。
4、其他
在ScheduledTaskRegistrar类中定义了根据三种不同类型的Task执行的四个方法：
Task类型有：
- CronTask
- TriggerTask
- IntervalTask
方法：
-
ScheduledTask scheduleCronTask(CronTask task);
- ScheduledFuture<?> schedule(Runnable task, Trigger trigger);
- ScheduledFuture<?> schedule(Runnable task, Date startTime);
-
ScheduledTask scheduleTriggerTask(TriggerTask task);
- ScheduledFuture<?> schedule(Runnable task, Trigger trigger);
- ScheduledFuture<?> schedule(Runnable task, Date startTime);
-
ScheduledTask scheduleFixedRateTask(IntervalTask task);
- ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long period);
- ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Date startTime, long period);
-
ScheduledTask scheduleFixedDelayTask(IntervalTask task);
- ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay);
- ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Date startTime, long delay);
其中重载方法取决于有没有设置initial-delay属性。
对于schedule的两个重载方法，
- 如果设置了initial-delay属性，则执行ScheduledExecutorService对象的schedule方法；
- 如果未设置则执行ReschedulingRunnable对象的schedule方法
对于另外四个方法，都是执行ScheduledExecutorService各自的scheduleXxx同名方法。
5、Spring Boot中使用Schedule
只要在主入口类上加入@EnableScheduling 即可启动任务调度了。
@Import(SchedulingConfiguration.class)
public @interface EnableScheduling {}
其中导入了SchedulingConfiguration类。
@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();
}
}
在SchedulingConfiguration类中，创建了一个ScheduledAnnotationBeanPostProcessor的Bean。看过上文的小伙伴肯定就熟悉这个类了，在讲解使用注解的时候，在AnnotationDrivenBeanDefinitionParser解析<task:annotation-driven />的类中会创建一个ScheduledAnnotationBeanPostProcessor的Bean，后续的过程就同使用注解的方式一样了。
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