这两天应用Scheduled注解来解决定时问题的时候，发现不能失常应用。所以就有了这一篇博客
@Scheduled(initialDelay = 2000,fixedDelay = 1000)
private void test(){
System.out.println(Math.random());
}单从源码的doc文件中能够看到这么一段
You can add the `@Scheduled` annotation to a method, along with trigger metadata. For
example, the following method is invoked every five seconds with a fixed delay,
meaning that the period is measured from the completion time of each preceding
invocation:
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@Scheduled(fixedDelay=5000)
public void doSomething() {
// something that should run periodically
}
----将源码放进我的环境运行，发现并不能失效。那就只能先看看源码来看看它到底是怎么失效的
注解Scheduled的源码
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
String CRON_DISABLED = ScheduledTaskRegistrar.CRON_DISABLED;
String cron() default "";
String zone() default "";
long fixedDelay() default -1;
String fixedDelayString() default "";
long fixedRate() default -1;
String fixedRateString() default "";
long initialDelay() default -1;
String initialDelayString() default "";
}而后，动静加载的代码在 ScheduledAnnotationBeanPostProcessor 的 postProcessAfterInitialization 办法中
@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> 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;
}首先，通过AopProxyUtils.ultimateTargetClass获取传入的Bean的最终类（是哪个类），而后判断以后类有没有在this.nonAnnotatedClasses中，如果没有在，则持续应用AnnotationUtils.isCandidateClass判断以后类是不是一个非抽象类或者接口，如果都满足，则调用
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);
});获取到某个办法的所有Scheduled。也就是说，一个办法，是能够同时被屡次定义周期化的。也就是这样
@Scheduled(fixedDelay = 5000)
@Schedules({@Scheduled(fixedDelay = 5000),@Scheduled(fixedDelay = 3000)})
public void test(){
logger.info("123");
}持续剖析源码，咱们能够发现，在失去targetClass（指标类）的所有带有@Scheduled或者@Schedules注解的办法并放到annotatedMethods中后，如果annotatedMethods的大小为0，则将以后指标targetClass放到this.nonAnnotatedClasses中，标记这个类中没有被相干注解润饰，不便新的调用方进行判断。如果annotatedMethods的大小不为空，则
nnotatedMethods.forEach((method, scheduledMethods) ->
scheduledMethods.forEach(scheduled -> processScheduled(scheduled, method, bean)));将独自解决每个周期性工作。上面来看看到底是怎么解决的
protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
// 能够看见，scheduled method的运行必须在Bean环境中，所以用@Schedules或者@Scheduled的办法必须在一个bean类外面
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 定义开始工夫
long initialDelay = scheduled.initialDelay();
String initialDelayString = scheduled.initialDelayString();
// initialDelay 和 initialDelayString 只能同时定义一个
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) {
// 调用 this.embeddedValueResolver.resolveStringValue 解析cron
cron = this.embeddedValueResolver.resolveStringValue(cron);
zone = this.embeddedValueResolver.resolveStringValue(zone);
}
if (StringUtils.hasLength(cron)) {
// 如果在initialDelay定义的状况下，cron是不失效的
Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
processedSchedule = true;
// String CRON_DISABLED = ScheduledTaskRegistrar.CRON_DISABLED;
// public static final String CRON_DISABLED = "-";
// 如果cron不等于 '-'
if (!Scheduled.CRON_DISABLED.equals(cron)) {
TimeZone timeZone;
// 解析timeZone
if (StringUtils.hasText(zone)) {
timeZone = StringUtils.parseTimeZoneString(zone);
}
else {
timeZone = TimeZone.getDefault();
}
// 应用 new CronTrigger(cron, timeZone) 创立定时触发器
// 应用 new CronTask(runnable, new CronTrigger(cron, timeZone)) 创立一个定时工作，定时触发器会触发runnable
// 调用 this.registrar.scheduleCronTask 注册工作到以后环境中
// tasks是一个汇合，防止反复注册雷同的工作
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) {
// 如果当前任务没有被退出到tasks
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
// 应用 new FixedDelayTask(runnable, fixedDelay, initialDelay) 来注册提早工作
tasks.add(this.registrar.scheduleFixedDelayTask(new FixedDelayTask(runnable, fixedDelay, initialDelay)));
}
String fixedDelayString = scheduled.fixedDelayString();
if (StringUtils.hasText(fixedDelayString)) {
// 如果没有传fixedDelay，然而传了fixedDelayString，能够应用它的值
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
// 如果下面的都没满足，则判断fixedDate和fixedDateString的值
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
// 同步的注册工作 退出缓存，方便使用
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());
}
}上面为某个类外面的办法是创立Runnabled的办法，传入办法和指标类就能够失去
protected Runnable createRunnable(Object target, Method method) {
Assert.isTrue(method.getParameterCount() == 0, "Only no-arg methods may be annotated with @Scheduled");
Method invocableMethod = AopUtils.selectInvocableMethod(method, target.getClass());
return new ScheduledMethodRunnable(target, invocableMethod);
}上面是scheduleCronTask办法的定义，能够看见这里会对task去重
@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);
}通过processScheduled办法会将某个被@Scheduled或者@Schedules注解润饰的办法注册进全局的scheduledTask环境中。
也就是说，办法postProcessAfterInitialization会将整个bean中的所有被@Scheduled或者@Schedules注解润饰的办法都注册进全局定时执行环境。
哪些地方调用了postProcessAfterInitialization
眼帘移到抽象类AbstractAutowireCapableBeanFactory的applyBeanPostProcessorsAfterInitialization办法中，这里是源码中惟一调用postProcessAfterInitialization的中央，也就是说，所有的周期工作都是在这里被注入到环境中的（其实不只是被@Scheduled或者@Schedules润饰的周期性工作）
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}那么既然来了，咱们还是剖析一下，这里到底做了什么。
首先，通过调用getBeanPostProcessors()获取到了所有的BeanPostProcessor，这个类能够了解为是各种Bean的加载器。而咱们的ScheduledAnnotationBeanPostProcessor就是其中之一。依据调用栈能够发现，最终追溯到了AbstractBeanFactory.beanPostProcessors（List\<BeanPostProcessor>类型），上面两个办法是增加函数
@Override
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
// Remove from old position, if any
this.beanPostProcessors.remove(beanPostProcessor);
// Add to end of list
this.beanPostProcessors.add(beanPostProcessor);
}
public void addBeanPostProcessors(Collection<? extends BeanPostProcessor> beanPostProcessors) {
this.beanPostProcessors.removeAll(beanPostProcessors);
this.beanPostProcessors.addAll(beanPostProcessors);
}能够看进去，beanPostProcessors中没有反复的Processors。咱们把下面那个函数定义为办法一，前面那个办法定义为办法二，办法二在上面这个办法中被调用了，整个调用栈如下：
private static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
if (beanFactory instanceof AbstractBeanFactory) {
// Bulk addition is more efficient against our CopyOnWriteArrayList there
((AbstractBeanFactory) beanFactory).addBeanPostProcessors(postProcessors);
}
else {
for (BeanPostProcessor postProcessor : postProcessors) {
beanFactory.addBeanPostProcessor(postProcessor);
}
}
}
这四次调用都呈现在同一个函数registerBeanPostProcessors中，那么咱们能够假如，这里的调用程序，就是Bean加载的先后顺序（做java开发的应该都晓得，如果代码写得不当，定义了谬误的Bean加载程序回导致注入无奈实现，从而造成代码无奈运行的问题）。那么，Bean的注册程序就是
priorityOrderedPostProcessors > orderedPostProcessors > nonOrderedPostProcessors > internalPostProcessors
registerBeanPostProcessors的源码剖析与题目没有什么关系，这里就不做剖析了。留着下次剖析Bean的时候再仔细分析。
从调用方剖析的路走不通，咱们能够尝试从最远头登程
咱们都晓得，应用@Scheduled或者@Schedules之前，必须要在全局加上@EnableScheduling的注解。那么咱们就能够从这个注解动手进行剖析。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {
}惋惜的是，源码中并没有对注解@EnableScheduling进行解析的代码。可是这是为什么呢？咱们留神到，润饰这个注解的有一个咱们素来没有见过的注解@Import，会不会是@Import
其中，@Import的源码如下
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
Class<?>[] value();
}其中，定义@Import注解行为的源码在类ConfigurationClassParser的collectImports办法中，来看看吧
private void collectImports(SourceClass sourceClass, Set<SourceClass> imports, Set<SourceClass> visited)
throws IOException {
if (visited.add(sourceClass)) {
for (SourceClass annotation : sourceClass.getAnnotations()) {
String annName = annotation.getMetadata().getClassName();
if (!annName.equals(Import.class.getName())) {
collectImports(annotation, imports, visited);
}
}
imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value"));
}
}这个函数是一个递归函数，会一直地查找某个注解以及润饰它的注解所有被Import注解导入的配置文件。这个函数的调用栈如下
private Set<SourceClass> getImports(SourceClass sourceClass) throws IOException {
Set<SourceClass> imports = new LinkedHashSet<>();
Set<SourceClass> visited = new LinkedHashSet<>();
collectImports(sourceClass, imports, visited);
return imports;
}
// getImports在ConfigurationClassParser的doProcessConfigurationClass办法中被调用
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
// doProcessConfigurationClass在ConfigurationClassParser的processConfigurationClass办法中被调用
do {
sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
}
while (sourceClass != null);
this.configurationClasses.put(configClass, configClass);
因为调用栈切实是太深，最初会到FrameworkServlet的refresh()办法上，临时我只能下一个论断就是，在Application的主类下面润饰的注解并不会独自写反射办法来实现，而是会通过spring提供的对立解决形式进行解决。因为在整个spring框架源码中都没有找到对该注解进行反射操作的内容。
总结
通过这一篇文章，咱们从源码中学习了@Scheduled 和 @Schedules 这两个注解的，他们是如何解析参数，如何退出工夫触发器，不过目前还欠缺工夫触发器到底是如何工作的这部分的内容，后续我会补上。
另外，咱们也首次理解了，这种注解是如何被spring框架调用到的，晓得了BeanFactory，也晓得了ConfigurationClassParser，这给咱们接下来全面钻研Spring容器这一块提供了契机。
最初的最初，我代码外面的问题就是没有在主类外面加@EnableScheduling注解
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