在 Java 應用程序中計劃重復執行的任務

package org.tiling.scheduling.examples;

import java.util.Timer;
import java.util.TimerTask;

public class EggTimer {
private final Timer timer = new Timer();
private final int minutes;

public EggTimer(int minutes) {
this.minutes = minutes;
}

public void start() {
timer.schedule(new TimerTask() {
public void run() {
playSound();
timer.cancel();
}
private void playSound() {
System.out.println("Your egg is ready!");
// Start a new thread to play a sound...
}
}, minutes * 60 * 1000);
}

public static void main(String[] args) {
EggTimer eggTimer = new EggTimer(2);
eggTimer.start();
}

}

package org.tiling.scheduling.examples;

import java.text.SimpleDateFormat;

import java.util.Date;

import org.tiling.scheduling.Scheduler;
import org.tiling.scheduling.SchedulerTask;
import org.tiling.scheduling.examples.iterators.DailyIterator;

public class AlarmClock {

private final Scheduler scheduler = new Scheduler();
private final SimpleDateFormat dateFormat =
new SimpleDateFormat("dd MMM yyyy HH:mm:ss.SSS");
private final int hourOfDay, minute, second;

public AlarmClock(int hourOfDay, int minute, int second) {
this.hourOfDay = hourOfDay;
this.minute = minute;
this.second = second;
}

public void start() {
scheduler.schedule(new SchedulerTask() {
public void run() {
soundAlarm();
}
private void soundAlarm() {
System.out.println("Wake up! " +
"It′s " + dateFormat.format(new Date()));
// Start a new thread to sound an alarm...
}
}, new DailyIterator(hourOfDay, minute, second));
}

public static void main(String[] args) {
AlarmClock alarmClock = new AlarmClock(7, 0, 0);
alarmClock.start();
}
}

package org.tiling.scheduling;

import java.util.Date;

public interface ScheduleIterator {
public Date next();
}

package org.tiling.scheduling.examples.iterators;

import org.tiling.scheduling.ScheduleIterator;

import java.util.Calendar;
import java.util.Date;

/**
* A DailyIterator class returns a sequence of dates on subsequent days
* representing the same time each day.
*/
public class DailyIterator implements ScheduleIterator {
private final int hourOfDay, minute, second;
private final Calendar calendar = Calendar.getInstance();

public DailyIterator(int hourOfDay, int minute, int second) {
this(hourOfDay, minute, second, new Date());
}

public DailyIterator(int hourOfDay, int minute, int second, Date date) {
this.hourOfDay = hourOfDay;
this.minute = minute;
this.second = second;
calendar.setTime(date);
calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
calendar.set(Calendar.MINUTE, minute);
calendar.set(Calendar.SECOND, second);
calendar.set(Calendar.MILLISECOND, 0);
if (!calendar.getTime().before(date)) {
calendar.add(Calendar.DATE, -1);
}
}

public Date next() {
calendar.add(Calendar.DATE, 1);
return calendar.getTime();
}

}

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);
}
}
}
}

}

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();
}
}

}