浅谈java定时任务：TimerTask

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java 定时任务TimerTask

定时任务有很多种实现，网上也有很多开源的定时任务框架可以参考，但博主只简单介绍一下博主使用到的四种定时任务的实现：Timer和TimerTaks、spring、quartz、spring和quartz。话不多说，直接上代码

Timer和TimerTask

我们先来看看Timer的源码

   public void schedule(TimerTask task, Date firstTime, long period) {        if (period <= 0)            throw new IllegalArgumentException("Non-positive period.");        sched(task, firstTime.getTime(), -period);    }

task是继承了TimerTask的自定义任务，firstTime:第一次执行时间 period：执行周期
再来看看Timer的构造方法

//Timer提供了四个构造方法，以此为例 public Timer(String name, boolean isDaemon) {        thread.setName(name);        thread.setDaemon(isDaemon);        thread.start();    }

可以看到Timer是基于线程的，isDaemon是否设置为守护进程
来看看start干了什么

public synchronized void start() {        //如果线程已经运行则抛出异常        if (threadStatus != 0)            throw new IllegalThreadStateException();        //将此线程加入到线程队列        group.add(this);        boolean started = false;        try {            start0();            started = true;        } finally {            try {                if (!started) {                    group.threadStartFailed(this);                }            } catch (Throwable ignore) {            }        }    }  //然而start0并没有做什么事情，可见，start只是将线程放入线程队列  private native void start0();

然而Timer就提供了四个不同作用的方法：构造方法、shcedule、cancel、purge

回归到核心方法schedule,我们来看看sched:

 private void sched(TimerTask task, long time, long period) {        if (time < 0)            throw new IllegalArgumentException("Illegal execution time.");        if (Math.abs(period) > (Long.MAX_VALUE >> 1))            period >>= 1;        synchronized(queue) {            if (!thread.newTasksMayBeScheduled)                throw new IllegalStateException("Timer already cancelled.");            synchronized(task.lock) {            //如果这个线程每日一被初始化就抛出异常                if (task.state != TimerTask.VIRGIN)                    throw new IllegalStateException(                        "Task already scheduled or cancelled");                 //下次唤醒时间                task.nextExecutionTime = time;                task.period = period;                task.state = TimerTask.SCHEDULED;            }            //将当前线程加入队列尾部            queue.add(task);            //如果是对首就唤醒线程，执行TimerTask            if (queue.getMin() == task)                queue.notify();        }    }

继承了TimerTask的类只需要其run方法就好

  @Override    public void run() {        System.out.println("scheduleTask start :++++++++++++++++");    }

初始化这个类是就会启动任务

Timer和spring

定义一个类方法中调用timer的schedule，然后在spring启动时初始化这个方法即可

     public void executeTask() throws ParseException {        // 以每24小时执行一次        timer.schedule(                new TimerTask() {            @Override            public void run() {                    System.out.println("scheduleTask start :++++++++++++++++");        },  startTime, daySpan);    }

配置文件

<bean id="scheduleTask" class="com.task.ScheduleTask" init- method="executeTask"></bean>

TimerTask和Spring

实现继承了TimerTask的类的run方法，将调度任务交给spring

public class ScheduleTask  extends TimerTask{  @Override    public void run() {        System.out.println("scheduleTask start :++++++++++++++++");    }}

配置文件如下：

  <bean id="scheduleTask" class="com.task.ScheduleTask">  </bean>    <bean id="scheduledExecutorService"     class="org.springframework.scheduling.concurrent.ScheduledExecutorFactoryBean">        <property name="awaitTerminationSeconds" value="300"/>        <property name="continueScheduledExecutionAfterException" value="false"/>        <property name="poolSize" value="1"/>        <property name="scheduledExecutorTasks">            <list>                <ref bean="scheduledExecutorTask"/>            </list>        </property>        <property name="waitForTasksToCompleteOnShutdown" value="true"/>        <property name="threadPriority" value="1"/>    </bean>    <bean id="scheduledExecutorTask"    class="org.springframework.scheduling.concurrent.ScheduledExecutorTask">        <!--当有延迟执行的任务是否修正任务执行时-->        <property name="fixedRate" value="true"/>        <property name="period" value="1"/>        <!--每秒执行一次-->        <property name="timeUnit" value="MILLISECONDS"/>        <!--具体任务-->        <property name="runnable" ref="scheduleTask"/>    </bean>

这里看一下fixedRate的源码

protected void registerTasks(ScheduledExecutorTask[] tasks, ScheduledExecutorService executor) {        for (ScheduledExecutorTask task : tasks) {            Runnable runnable = getRunnableToSchedule(task);            if (task.isOneTimeTask()) {                executor.schedule(runnable, task.getDelay(), task.getTimeUnit());            }            else {                if (task.isFixedRate()) {                    executor.scheduleAtFixedRate(runnable, task.getDelay(), task.getPeriod(), task.getTimeUnit());                }                else {                    executor.scheduleWithFixedDelay(runnable, task.getDelay(), task.getPeriod(), task.getTimeUnit());                }            }        }    }

看不下去了以后再说~

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