Springboot定时任务的原理及动态创建详解

v一、前言

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定时任务一般是项目中都需要用到的,可以用于定时处理一些特殊的任务。这篇文章主要给大家介绍了关于Spring boot定时任务的原理及动态创建的相关内容，下面来一起看看详细的介绍吧

上周工作遇到了一个需求，同步多个省份销号数据，解绑微信粉丝。分省定时将销号数据放到SFTP服务器上，我需要开发定时任务去解析文件。因为是多省份，服务器、文件名规则、数据规则都不一定，所以要做成可配置是有一定难度的。数据规则这块必须强烈要求统一，服务器、文件名规则都可以从配置中心去读。每新增一个省份的配置，后台感知到后，动态生成定时任务。

v二、Springboot引入定时任务核心配置

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {

}

@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();
 }

}

接下来主要看一下这个核心后置处理器：ScheduledAnnotationBeanPostProcessor 。

@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)) {
 Map> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
  (MethodIntrospector.MetadataLookup>) method -> {
   Set 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;
}

1、处理Scheduled注解，通过ScheduledTaskRegistrar注册定时任务。

private void finishRegistration() {
 if (this.scheduler != null) {
 this.registrar.setScheduler(this.scheduler);
 }

 if (this.beanFactory instanceof ListableBeanFactory) {
 Map beans =
  ((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);
 List configurers = new ArrayList<>(beans.values());
 AnnotationAwareOrderComparator.sort(configurers);
 for (SchedulingConfigurer configurer : configurers) {
  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(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, false));
 }
 catch (NoUniqueBeanDefinitionException ex) {
  logger.trace("Could not find unique TaskScheduler bean", ex);
  try {
  this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, true));
  }
  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.trace("Could not find default TaskScheduler bean", ex);
  // Search for ScheduledExecutorService bean next...
  try {
  this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, false));
  }
  catch (NoUniqueBeanDefinitionException ex2) {
  logger.trace("Could not find unique ScheduledExecutorService bean", ex2);
  try {
   this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, true));
  }
  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.trace("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();
}

1、通过一系列的SchedulingConfigurer动态配置ScheduledTaskRegistrar。

2、向ScheduledTaskRegistrar注册一个TaskScheduler（用于对Runnable的任务进行调度，它包含有多种触发规则）。

3、registrar.afterPropertiesSet()，在这开始安排所有的定时任务开始执行了。

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));
 }
 }
}

1、TriggerTask：动态定时任务。通过Trigger#nextExecutionTime 给定的触发上下文确定下一个执行时间。

2、CronTask：动态定时任务，TriggerTask子类。通过cron表达式确定的时间触发下一个任务执行。

3、IntervalTask：一定时间延迟之后，周期性执行的任务。

4、taskScheduler 如果为空，默认是ConcurrentTaskScheduler，并使用默认单线程的ScheduledExecutor。

v三、主要看一下CronTask工作原理

ScheduledTaskRegistrar.java
@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);
}

ConcurrentTaskScheduler.java
@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.scheduledExecutor, errorHandler).schedule();
 }
 }
 catch (RejectedExecutionException ex) {
 throw new TaskRejectedException("Executor [" + this.scheduledExecutor + "] did not accept task: " + task, ex);
 }
}

ReschedulingRunnable.java
@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() - System.currentTimeMillis();
 this.currentFuture = this.executor.schedule(this, initialDelay, TimeUnit.MILLISECONDS);
 return this;
 }
}

private ScheduledFuture<?> obtainCurrentFuture() {
 Assert.state(this.currentFuture != null, "No scheduled future");
 return this.currentFuture;
}

@Override
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();
 }
 }
}

1、最终将task和trigger都封装到了ReschedulingRunnable中。

2、ReschedulingRunnable实现了任务重复调度（schedule方法中调用调度器executor并传入自身对象，executor会调用run方法，run方法又调用了schedule方法）。

3、ReschedulingRunnable schedule方法加了同步锁，只能有一个线程拿到下次执行时间并加入执行器的调度。

4、不同的ReschedulingRunnable对象之间在线程池够用的情况下是不会相互影响的，也就是说满足线程池的条件下，TaskScheduler的schedule方法的多次调用是可以交叉执行的。

ScheduledThreadPoolExecutor.java
public ScheduledFuture<?> schedule(Runnable command,
     long delay,
     TimeUnit unit) {
 if (command == null || unit == null)
 throw new NullPointerException();
 RunnableScheduledFuture<?> t = decorateTask(command,
 new ScheduledFutureTask(command, null,
     triggerTime(delay, unit)));
 delayedExecute(t);
 return t;
}


private void delayedExecute(RunnableScheduledFuture<?> task) {
 if (isShutdown())
 reject(task);
 else {
 super.getQueue().add(task);
 if (isShutdown() &&
  !canRunInCurrentRunState(task.isPeriodic()) &&
  remove(task))
  task.cancel(false);
 else
  ensurePrestart();
 }
}

ScheduledFutureTask 工作原理如下图所示【太懒了，不想画图了，盗图一张】。

Spring boot定时任务的原理及动态创建详解　

1、ScheduledFutureTask会放入优先阻塞队列：ScheduledThreadPoolExecutor.DelayedWorkQueue（二叉最小堆实现）

2、上图中的Thread对象即ThreadPoolExecutor.Worker，实现了Runnable接口

/**
 * Creates with given first task and thread from ThreadFactory.
 * @param firstTask the first task (null if none)
 */
Worker(Runnable firstTask) {
 setState(-1); // inhibit interrupts until runWorker
 this.firstTask = firstTask;
 this.thread = getThreadFactory().newThread(this);
}

/** Delegates main run loop to outer runWorker */
public void run() {
 runWorker(this);
}

1、Worker中维护了Thread对象，Thread对象的Runnable实例即Worker自身

2、ThreadPoolExecutor#addWorker方法中会创建Worker对象，然后拿到Worker中的thread实例并start，这样就创建了线程池中的一个线程实例

3、Worker的run方法会调用ThreadPoolExecutor#runWorker方法，这才是任务最终被执行的地方，该方法示意如下

（1）首先取传入的task执行，如果task是null，只要该线程池处于运行状态，就会通过getTask方法从workQueue中取任务。ThreadPoolExecutor的execute方法会在无法产生core线程的时候向　　workQueue队列中offer任务。
getTask方法从队列中取task的时候会根据相关配置决定是否阻塞和阻塞多久。如果getTask方法结束，返回的是null，runWorker循环结束，执行processWorkerExit方法。
至此，该线程结束自己的使命，从线程池中“消失”。

（2）在开始执行任务之前，会调用Worker的lock方法，目的是阻止task正在被执行的时候被interrupt，通过调用clearInterruptsForTaskRun方法来保证的(后面可以看一下这个方法)，该线程没有自己的interrupt set了。

（3）beforeExecute和afterExecute方法用于在执行任务前后执行一些自定义的操作，这两个方法是空的，留给继承类去填充功能。

我们可以在beforeExecute方法中抛出异常，这样task不会被执行，而且在跳出该循环的时候completedAbruptly的值是true，表示the worker died due to user exception，会用decrementWorkerCount调整wc。

（4）因为Runnable的run方法不能抛出Throwables异常，所以这里重新包装异常然后抛出，抛出的异常会使当当前线程死掉，可以在afterExecute中对异常做一些处理。

（5）afterExecute方法也可能抛出异常，也可能使当前线程死掉。

v四、动态创建定时任务

v　　TaskConfiguration 配置类

@Configuration
@EnableScheduling
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class TaskConfiguration {

 @Bean(name = ScheduledAnnotationBeanPostProcessor.DEFAULT_TASK_SCHEDULER_BEAN_NAME)
 @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
 public ScheduledExecutorService scheduledAnnotationProcessor() {
 return Executors.newScheduledThreadPool(5, new DefaultThreadFactory());
 }

 private static class DefaultThreadFactory implements ThreadFactory {
 private static final AtomicInteger poolNumber = new AtomicInteger(1);
 private final ThreadGroup group;
 private final AtomicInteger threadNumber = new AtomicInteger(1);
 private final String namePrefix;

 DefaultThreadFactory() {
  SecurityManager s = System.getSecurityManager();
  group = (s != null) ? s.getThreadGroup() :
   Thread.currentThread().getThreadGroup();
  namePrefix = "pool-" +
   poolNumber.getAndIncrement() +
   "-schedule-";
 }

 @Override
 public Thread newThread(Runnable r) {
  Thread t = new Thread(group, r,
   namePrefix + threadNumber.getAndIncrement(),
   0);
  if (t.isDaemon()) {
  t.setDaemon(false);
  }
  if (t.getPriority() != Thread.NORM_PRIORITY) {
  t.setPriority(Thread.NORM_PRIORITY);
  }
  return t;
 }
 }
}

1、保证ConcurrentTaskScheduler不使用默认单线程的ScheduledExecutor，而是corePoolSize=5的线程池

2、自定义线程池工厂类

v　　DynamicTask 动态定时任务

@Configuration
public class DynamicTask implements SchedulingConfigurer {
 private static Logger LOGGER = LoggerFactory.getLogger(DynamicTask.class);

 private static final ExecutorService es = new ThreadPoolExecutor(10, 20,
   0L, TimeUnit.MILLISECONDS,
   new LinkedBlockingQueue<>(10),
   new DynamicTaskConsumeThreadFactory());


 private volatile ScheduledTaskRegistrar registrar;
 private final ConcurrentHashMap> scheduledFutures = new ConcurrentHashMap<>();
 private final ConcurrentHashMap cronTasks = new ConcurrentHashMap<>();

 private volatile List taskConstants = Lists.newArrayList();

 @Override
 public void configureTasks(ScheduledTaskRegistrar registrar) {
  this.registrar = registrar;
  this.registrar.addTriggerTask(() -> {
     if (!CollectionUtils.isEmpty(taskConstants)) {
      LOGGER.info("检测动态定时任务列表...");
      List tts = new ArrayList<>();
      taskConstants
        .forEach(taskConstant -> {
         TimingTask tt = new TimingTask();
         tt.setExpression(taskConstant.getCron());
         tt.setTaskId("dynamic-task-" + taskConstant.getTaskId());
         tts.add(tt);
        });
      this.refreshTasks(tts);
     }
    }
    , triggerContext -> new PeriodicTrigger(5L, TimeUnit.SECONDS).nextExecutionTime(triggerContext));
 }


 public List getTaskConstants() {
  return taskConstants;
 }

 private void refreshTasks(List tasks) {
  //取消已经删除的策略任务
  Set taskIds = scheduledFutures.keySet();
  for (String taskId : taskIds) {
   if (!exists(tasks, taskId)) {
    scheduledFutures.get(taskId).cancel(false);
   }
  }
  for (TimingTask tt : tasks) {
   String expression = tt.getExpression();
   if (StringUtils.isBlank(expression) || !CronSequenceGenerator.isValidExpression(expression)) {
    LOGGER.error("定时任务DynamicTask cron表达式不合法: " + expression);
    continue;
   }
   //如果配置一致，则不需要重新创建定时任务
   if (scheduledFutures.containsKey(tt.getTaskId())
     && cronTasks.get(tt.getTaskId()).getExpression().equals(expression)) {
    continue;
   }
   //如果策略执行时间发生了变化，则取消当前策略的任务
   if (scheduledFutures.containsKey(tt.getTaskId())) {
    scheduledFutures.remove(tt.getTaskId()).cancel(false);
    cronTasks.remove(tt.getTaskId());
   }
   CronTask task = new CronTask(tt, expression);
   ScheduledFuture<?> future = registrar.getScheduler().schedule(task.getRunnable(), task.getTrigger());
   cronTasks.put(tt.getTaskId(), task);
   scheduledFutures.put(tt.getTaskId(), future);
  }
 }

 private boolean exists(List tasks, String taskId) {
  for (TimingTask task : tasks) {
   if (task.getTaskId().equals(taskId)) {
    return true;
   }
  }
  return false;
 }

 @PreDestroy
 public void destroy() {
  this.registrar.destroy();
 }

 public static class TaskConstant {
  private String cron;
  private String taskId;

  public String getCron() {
   return cron;
  }

  public void setCron(String cron) {
   this.cron = cron;
  }

  public String getTaskId() {
   return taskId;
  }

  public void setTaskId(String taskId) {
   this.taskId = taskId;
  }
 }

 private class TimingTask implements Runnable {
  private String expression;

  private String taskId;

  public String getTaskId() {
   return taskId;
  }

  public void setTaskId(String taskId) {
   this.taskId = taskId;
  }

  @Override
  public void run() {
   //设置队列大小10
   LOGGER.error("当前CronTask: " + this);
   DynamicBlockingQueue queue = new DynamicBlockingQueue(3);
   es.submit(() -> {
    while (!queue.isDone() || !queue.isEmpty()) {
     try {
      String content = queue.poll(500, TimeUnit.MILLISECONDS);
      if (StringUtils.isBlank(content)) {
       return;
      }
      LOGGER.info("DynamicBlockingQueue 消费：" + content);
      TimeUnit.MILLISECONDS.sleep(500);
     } catch (InterruptedException e) {
      e.printStackTrace();
     }
    }
   });

   //队列放入数据
   for (int i = 0; i < 5; ++i) {
    try {
     queue.put(String.valueOf(i));
     LOGGER.info("DynamicBlockingQueue 生产：" + i);
    } catch (InterruptedException e) {
     e.printStackTrace();
    }
   }
   queue.setDone(true);
  }

  public String getExpression() {
   return expression;
  }

  public void setExpression(String expression) {
   this.expression = expression;
  }

  @Override
  public String toString() {
   return ReflectionToStringBuilder.toString(this
     , ToStringStyle.JSON_STYLE
     , false
     , false
     , TimingTask.class);
  }

 }

 /**
  * 队列消费线程工厂类
  */
 private static class DynamicTaskConsumeThreadFactory implements ThreadFactory {
  private static final AtomicInteger poolNumber = new AtomicInteger(1);
  private final ThreadGroup group;
  private final AtomicInteger threadNumber = new AtomicInteger(1);
  private final String namePrefix;

  DynamicTaskConsumeThreadFactory() {
   SecurityManager s = System.getSecurityManager();
   group = (s != null) ? s.getThreadGroup() :
     Thread.currentThread().getThreadGroup();
   namePrefix = "pool-" +
     poolNumber.getAndIncrement() +
     "-dynamic-task-";
  }

  @Override
  public Thread newThread(Runnable r) {
   Thread t = new Thread(group, r,
     namePrefix + threadNumber.getAndIncrement(),
     0);
   if (t.isDaemon()) {
    t.setDaemon(false);
   }
   if (t.getPriority() != Thread.NORM_PRIORITY) {
    t.setPriority(Thread.NORM_PRIORITY);
   }
   return t;
  }
 }

 private static class DynamicBlockingQueue extends LinkedBlockingQueue {
  DynamicBlockingQueue(int capacity) {
   super(capacity);
  }


  private volatile boolean done = false;

  public boolean isDone() {
   return done;
  }

  public void setDone(boolean done) {
   this.done = done;
  }
 }
}

1、taskConstants 动态任务列表

2、ScheduledTaskRegistrar#addTriggerTask 添加动态周期定时任务，检测动态任务列表的变化

CronTask task = new CronTask(tt, expression);
ScheduledFuture<?> future = registrar.getScheduler().schedule(task.getRunnable(), task.getTrigger());
cronTasks.put(tt.getTaskId(), task);
scheduledFutures.put(tt.getTaskId(), future);

3、动态创建cron定时任务，拿到ScheduledFuture实例并缓存起来

4、在刷新任务列表时，通过缓存的ScheduledFuture实例和CronTask实例，来决定是否取消、移除失效的动态定时任务。

v　　DynamicTaskTest 动态定时任务测试类

@RunWith(SpringRunner.class)
@SpringBootTest
public class DynamicTaskTest {

 @Autowired
 private DynamicTask dynamicTask;

 @Test
 public void test() throws InterruptedException {
  List taskConstans = dynamicTask.getTaskConstants();
  DynamicTask.TaskConstant taskConstant = new DynamicTask.TaskConstant();
  taskConstant.setCron("0/5 * * * * ?");
  taskConstant.setTaskId("test1");
  taskConstans.add(taskConstant);


  DynamicTask.TaskConstant taskConstant1 = new DynamicTask.TaskConstant();
  taskConstant1.setCron("0/5 * * * * ?");
  taskConstant1.setTaskId("test2");
  taskConstans.add(taskConstant1);

  DynamicTask.TaskConstant taskConstant2 = new DynamicTask.TaskConstant();
  taskConstant2.setCron("0/5 * * * * ?");
  taskConstant2.setTaskId("test3");
  taskConstans.add(taskConstant2);

  TimeUnit.SECONDS.sleep(40);
  //移除并添加新的配置
  taskConstans.remove(taskConstans.size() - 1);
  DynamicTask.TaskConstant taskConstant3 = new DynamicTask.TaskConstant();
  taskConstant3.setCron("0/5 * * * * ?");
  taskConstant3.setTaskId("test4");
  taskConstans.add(taskConstant3);
//
  TimeUnit.MINUTES.sleep(50);
 }
}

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对创新互联的支持。

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