Springboot定时任务原理及如何动态创建定时任务

一、前言

　　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。

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<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;
}

　　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<String, SchedulingConfigurer> beans =
                ((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);
        List<SchedulingConfigurer> 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。

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<Void>(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】。

　　 

　　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。

四、动态创建定时任务

　　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

　　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<String, ScheduledFuture<?>> scheduledFutures = new ConcurrentHashMap<>();
    private final ConcurrentHashMap<String, CronTask> cronTasks = new ConcurrentHashMap<>();

    private volatile List<TaskConstant> 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<TimingTask> 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<TaskConstant> getTaskConstants() {
        return taskConstants;
    }

    private void refreshTasks(List<TimingTask> tasks) {
        //取消已经删除的策略任务
        Set<String> 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<TimingTask> 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<String> {
        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。

　　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<DynamicTask.TaskConstant> 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);
    }
}