JAVA定时任务怎么实现

class="prettyprint hljs gradle" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">1. 所有已注册task
org.springframework.scheduling.config.ScheduledTaskRegistrar
protected void scheduleTasks() {
    ...
    if (this.triggerTasks != null) {
        for (TriggerTask task : this.triggerTasks) {
            // 执行初始化完成的task和Trigger
            this.scheduledFutures.add(this.taskScheduler.schedule(
                    task.getRunnable(), task.getTrigger()));
        }
    }
    ...
}
 
2. 单个task
org.springframework.scheduling.TaskScheduler
ScheduledFuture schedule(Runnable task, Trigger trigger);
 
3. 线程池执行task
org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler
public ScheduledFuture schedule(Runnable task, Trigger trigger) {
    ScheduledExecutorService executor = getScheduledExecutor();
    try {
        ErrorHandler errorHandler =
                (this.errorHandler != null ? this.errorHandler : TaskUtils.getDefaultErrorHandler(true));
        // 调用具体的实现方法.schedule()
        return new ReschedulingRunnable(task, trigger, executor, errorHandler).schedule();
    }
    catch (RejectedExecutionException ex) {
        throw new TaskRejectedException("Executor [" + executor + "] did not accept task: " + task, ex);
    }
}
 
4. 这块是具体的线程实现细节，已经与schedul无关
private  ScheduledFuture schedule(final ScheduledFutureTask task) {
    if (task == null) {
        throw new NullPointerException("task");
    } else {
        if (this.inEventLoop()) {
            this.delayedTaskQueue.add(task);
        } else {
            // 此处就是真正的线程执行方法
            this.execute(new Runnable() {
                public void run() {
                    SingleThreadEventExecutor.this.delayedTaskQueue.add(task);
                }
            });
        }
 
        return task;
    }
}

1.2.3 @Scheduled注解的生效原理

class="prettyprint hljs gradle" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor
 
// BeanPostProcessor生命周期方法，spring加载的时候会执行
public Object postProcessAfterInitialization(final Object bean, String beanName) {
        Class targetClass = AopUtils.getTargetClass(bean);
    if (!this.nonAnnotatedClasses.containsKey(targetClass)) {
        final Set<Method> annotatedMethods = new LinkedHashSet<Method>(1);
        ReflectionUtils.doWithMethods(targetClass, new MethodCallback() {
            public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
                Scheduled scheduled = AnnotationUtils.getAnnotation(method, Scheduled.class);
                if (scheduled != null) {
                    // @Scheduled的真正解析方法，具体解析细节和参数参看源码
                    // 解析后添加到ScheduledTaskRegistrar里
                    // 全部任务解析完成，执行ScheduledTaskRegistrar，具体实现参看[1.2.2 调用链路]章节
                    processScheduled(scheduled, method, bean);
                    annotatedMethods.add(method);
                }
            }
        });
        if (annotatedMethods.isEmpty()) {
            this.nonAnnotatedClasses.put(targetClass, Boolean.TRUE);
        }
    }
    return bean;
}

二、QUARTZ

2.1 使用方法

class="prettyprint hljs fsharp" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">// 实例化一个调度器工厂，每个应用只有唯一一个工厂实例
SchedulerFactory schedFact = new org.quartz.impl.StdSchedulerFactory();
// 实例化一个调度器
Scheduler sched = schedFact.getScheduler();
// 启动，只有启动了调度器Quartz才会去执行任务
sched.start();
 
// 实例化一个任务
JobDetail job = newJob(HelloJob.class)
  .withIdentity("myJob", "group1")
  .build();
 
// 实例化一个任务触发器,立刻触发，每40s执行一次
Trigger trigger = newTrigger()
  .withIdentity("myTrigger", "group1")
  .startNow()
  .withSchedule(simpleSchedule()
      .withIntervalInSeconds(40)
      .repeatForever())
  .build();
 
// 调度任务
sched.scheduleJob(job, trigger);

2.2 源码分析

2.2.1 启动入口

class="prettyprint hljs xml" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">1\. web.xml配置
   <param-name>quartz:config-fileparam-name>
   <param-value>/some/path/my_quartz.propertiesparam-value>
<context-param>
   <param-name>quartz:shutdown-on-unloadparam-name>
   <param-value>trueparam-value>
context-param>
<context-param>
   <param-name>quartz:start-on-loadparam-name>
   <param-value>trueparam-value>
context-param>
 
<listener>
   <listener-class>
       org.quartz.ee.servlet.QuartzInitializerListener
   listener-class>
listener>
 
2\. org.quartz.ee.servlet.QuartzInitializerListener
// 执行ServletContextListener.contextInitialized的容器生命周期方法
public void contextInitialized(ServletContextEvent sce) {
    ...
    // 根据自定义的配置文件加载SchedulerFactory
    if (configFile != null) {
        factory = new StdSchedulerFactory(configFile);
    } else {
        factory = new StdSchedulerFactory();
    }
 
    // 加载scheduler
    scheduler = factory.getScheduler();
 
    // 启动scheduler
    scheduler.start();
    log.info("Scheduler has been started...");
    ...
}

2.2.2 核心方法详解

class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">1. StdSchedulerFactory.getScheduler()
public Scheduler getScheduler() throws SchedulerException {
    if (cfg == null) {
        // 根据不同的配置方式加载对应配置
        initialize();
    }
    ... 
    // 加载实例（加载Scheduler整个上下文环境）
    sched = instantiate();
    return sched;
}
 
2. StdSchedulerFactory.getScheduler().instantiate()
具体实现代码很多，以下做伪代码描述
private Scheduler instantiate() throws SchedulerException {
 
    // 校验初始化
    if (cfg == null) {
        initialize();
    }
 
    // 获取 Scheduler
    // 加载 ThreadPool
    // 加载 JobStore
    // 加载 DataSources
    // 加载 SchedulerPlugins
    // 加载 JobListeners
    // 加载 TriggerListeners
    // 加载 ThreadExecutor
 
    // 构造QuartzScheduler
    qs = new QuartzScheduler(rsrcs, schedCtxt, idleWaitTime, dbFailureRetry);
    Scheduler scheduler = instantiate(rsrcs, qs);
    qs.initialize();
 
    // 返回实例化好的scheduler
    return scheduler;
}