ScheduledExecutor 和 Calendar 实现复杂任务调度

Timer 和 ScheduledExecutor 都仅能提供基于开始时间与重复间隔的任务调度，不能胜任更加复杂的调度需求。比如，设置每星期二的 16:38:10 执行任务。该功能使用 Timer 和 ScheduledExecutor 都不能直接实现，但我们可以借助 Calendar 间接实现该功能。

清单 3. 使用 ScheduledExcetuor 和 Calendar 进行任务调度

package com.ibm.scheduler;

import java.util.Calendar;
import java.util.Date;
import java.util.TimerTask;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class ScheduledExceutorTest2 extends TimerTask {

	private String jobName = "";

	public ScheduledExceutorTest2(String jobName) {
		super();
		this.jobName = jobName;
	}

	@Override
	public void run() {
		System.out.println("Date = "+new Date()+", execute " + jobName);
	}

	/**
	 * 计算从当前时间currentDate开始，满足条件dayOfWeek, hourOfDay, 
	 * minuteOfHour, secondOfMinite的最近时间
	 * @return
	 */
	public Calendar getEarliestDate(Calendar currentDate, int dayOfWeek,
			int hourOfDay, int minuteOfHour, int secondOfMinite) {
		//计算当前时间的WEEK_OF_YEAR,DAY_OF_WEEK, HOUR_OF_DAY, MINUTE,SECOND等各个字段值
		int currentWeekOfYear = currentDate.get(Calendar.WEEK_OF_YEAR);
		int currentDayOfWeek = currentDate.get(Calendar.DAY_OF_WEEK);
		int currentHour = currentDate.get(Calendar.HOUR_OF_DAY);
		int currentMinute = currentDate.get(Calendar.MINUTE);
		int currentSecond = currentDate.get(Calendar.SECOND);

		//如果输入条件中的dayOfWeek小于当前日期的dayOfWeek,则WEEK_OF_YEAR需要推迟一周
		boolean weekLater = false;
		if (dayOfWeek < currentDayOfWeek) {
			weekLater = true;
		} else if (dayOfWeek == currentDayOfWeek) {
			//当输入条件与当前日期的dayOfWeek相等时，如果输入条件中的
			//hourOfDay小于当前日期的
			//currentHour，则WEEK_OF_YEAR需要推迟一周	
			if (hourOfDay < currentHour) {
				weekLater = true;
			} else if (hourOfDay == currentHour) {
                 //当输入条件与当前日期的dayOfWeek, hourOfDay相等时，
                 //如果输入条件中的minuteOfHour小于当前日期的
				//currentMinute，则WEEK_OF_YEAR需要推迟一周
				if (minuteOfHour < currentMinute) {
					weekLater = true;
				} else if (minuteOfHour == currentSecond) {
                     //当输入条件与当前日期的dayOfWeek, hourOfDay， 
                     //minuteOfHour相等时，如果输入条件中的
                    //secondOfMinite小于当前日期的currentSecond，
                    //则WEEK_OF_YEAR需要推迟一周
					if (secondOfMinite < currentSecond) {
						weekLater = true;
					}
				}
			}
		}
		if (weekLater) {
			//设置当前日期中的WEEK_OF_YEAR为当前周推迟一周
			currentDate.set(Calendar.WEEK_OF_YEAR, currentWeekOfYear + 1);
		}
		// 设置当前日期中的DAY_OF_WEEK,HOUR_OF_DAY,MINUTE,SECOND为输入条件中的值。
		currentDate.set(Calendar.DAY_OF_WEEK, dayOfWeek);
		currentDate.set(Calendar.HOUR_OF_DAY, hourOfDay);
		currentDate.set(Calendar.MINUTE, minuteOfHour);
		currentDate.set(Calendar.SECOND, secondOfMinite);
		return currentDate;

	}

	public static void main(String[] args) throws Exception {

		ScheduledExceutorTest2 test = new ScheduledExceutorTest2("job1");
		//获取当前时间
		Calendar currentDate = Calendar.getInstance();
		long currentDateLong = currentDate.getTime().getTime();
		System.out.println("Current Date = " + currentDate.getTime().toString());
		//计算满足条件的最近一次执行时间
		Calendar earliestDate = test
				.getEarliestDate(currentDate, 3, 16, 38, 10);
		long earliestDateLong = earliestDate.getTime().getTime();
		System.out.println("Earliest Date = "
				+ earliestDate.getTime().toString());
		//计算从当前时间到最近一次执行时间的时间间隔
		long delay = earliestDateLong - currentDateLong;
		//计算执行周期为一星期
		long period = 7 * 24 * 60 * 60 * 1000;
		ScheduledExecutorService service = Executors.newScheduledThreadPool(10);
		//从现在开始delay毫秒之后，每隔一星期执行一次job1
		service.scheduleAtFixedRate(test, delay, period,
				TimeUnit.MILLISECONDS);

	}
} 
Output:
Current Date = Wed Feb 02 17:32:01 CST 2011
Earliest Date = Tue Feb 8 16:38:10 CST 2011
Date = Tue Feb 8 16:38:10 CST 2011, execute job1
Date = Tue Feb 15 16:38:10 CST 2011, execute job1

  实现了每星期二 16:38:10 调度任务的功能。其核心在于根据当前时间推算出最近一个星期二 16:38:10 的绝对时间，然后计算与当前时间的时间差，作为调用 ScheduledExceutor 函数的参数。计算最近时间要用到 java.util.calendar 的功能。首先需要解释 calendar 的一些设计思想。Calendar 有以下几种唯一标识一个日期的组合方式：

 YEAR + MONTH + DAY_OF_MONTH 
 YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK 
 YEAR + MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK 
 YEAR + DAY_OF_YEAR 
 YEAR + DAY_OF_WEEK + WEEK_OF_YEAR 

 

上述组合分别加上 HOUR_OF_DAY + MINUTE + SECOND 即为一个完整的时间标识。本例采用了最后一种组合方式。输入为 DAY_OF_WEEK, HOUR_OF_DAY, MINUTE, SECOND 以及当前日期 , 输出为一个满足 DAY_OF_WEEK, HOUR_OF_DAY, MINUTE, SECOND 并且距离当前日期最近的未来日期。计算的原则是从输入的 DAY_OF_WEEK 开始比较，如果小于当前日期的 DAY_OF_WEEK，则需要向 WEEK_OF_YEAR 进一， 即将当前日期中的 WEEK_OF_YEAR 加一并覆盖旧值；如果等于当前的 DAY_OF_WEEK, 则继续比较 HOUR_OF_DAY；如果大于当前的 DAY_OF_WEEK，则直接调用 java.util.calenda 的 calendar.set(field, value) 函数将当前日期的 DAY_OF_WEEK, HOUR_OF_DAY, MINUTE, SECOND 赋值为输入值，依次类推，直到比较至 SECOND。读者可以根据输入需求选择不同的组合方式来计算最近执行时间。