Java语言中Timer类的简洁用法(二)

作者：xiaoxiao
发表时间：2020-12-23 10:38
来源：未知

实现计划框架在上一节，我们学习了如何使用计划框架，并将它与 Java 定时器框架进行了比较。下面，我将向您展示如何实现这个框架。除了清单 3 中展示的 ScheduleIterator 接口，构成这个框架的还有另外两个类 —— Scheduler 和 SchedulerTask 。这些类实际上在内部使用 Timer 和 SchedulerTask，因为计划其实就是一系列的单次定时器。

清单 5 和 6 显示了这两个类的源代码：清单 5. Scheduler

package org.tiling.scheduling; import java.util.Date; import java.util.Timer; import java.util.TimerTask; public class Scheduler { class SchedulerTimerTask extends TimerTask { private SchedulerTask schedulerTask; private ScheduleIterator iterator; public SchedulerTimerTask(SchedulerTask schedulerTask, ScheduleIterator iterator) { this.schedulerTask = schedulerTask; this.iterator = iterator; } public void run() { schedulerTask.run(); reschedule(schedulerTask, iterator); } } private final Timer timer = new Timer(); public Scheduler() { } public void cancel() { timer.cancel(); } public void schedule(SchedulerTask schedulerTask, ScheduleIterator iterator) { Date time = iterator.next(); if (time == null) { schedulerTask.cancel(); } else { synchronized(schedulerTask.lock) { if (schedulerTask.state != SchedulerTask.VIRGIN) { throw new IllegalStateException("Task already scheduled " + "or cancelled"); } schedulerTask.state = SchedulerTask.SCHEDULED; schedulerTask.timerTask = new SchedulerTimerTask(schedulerTask, iterator); timer.schedule(schedulerTask.timerTask, time); } } } private void reschedule(SchedulerTask schedulerTask, ScheduleIterator iterator) { Date time = iterator.next(); if (time == null) { schedulerTask.cancel(); } else { synchronized(schedulerTask.lock) { if (schedulerTask.state != SchedulerTask.CANCELLED) { schedulerTask.timerTask = new SchedulerTimerTask(schedulerTask, iterator); timer.schedule(schedulerTask.timerTask, time); } } } } }

清单 6 显示了 SchedulerTask 类的源代码：

package org.tiling.scheduling; import java.util.TimerTask; public abstract class SchedulerTask implements Runnable { final Object lock = new Object(); int state = VIRGIN; static final int VIRGIN = 0; static final int SCHEDULED = 1; static final int CANCELLED = 2; TimerTask timerTask; protected SchedulerTask() { } public abstract void run(); public boolean cancel() { synchronized(lock) { if (timerTask != null) { timerTask.cancel(); } boolean result = (state == SCHEDULED); state = CANCELLED; return result; } } public long scheduledExecutionTime() { synchronized(lock) { return timerTask == null ? 0 : timerTask.scheduledExecutionTime(); } } }