timer与ScheduledExecutorService

Timer和ScheduledExecutorService都可以用来做定时任务，有管理任务延迟执行("如1000ms后执行任务")以及周期性执行("如每500ms执行一次该任务")。但至从JDK1.5之后，建议采用ScheduledExecutorService。

原因如下：

1、Timer对调度的支持是基于绝对时间,而不是相对时间的，由此任务对系统时钟的改变是敏感的;但ScheduledThreadExecutor只支持相对时间。

2、如果TimerTask抛出未检查的异常，Timer将会产生无法预料的行为。Timer线程并不捕获异常，所以 TimerTask抛出的未检查的异常会终止timer线程。此时，已经被安排但尚未执行的TimerTask永远不会再执行了，新的任务也不能被调度了。

下面例子介绍了ScheduledExecutorService与Calendar的一个应用，用来解决一些复杂的时间问题，比如每个星期二的16点38分执行！当然如果采用spring的任务调度的话会简单得多

package com.qinsoft.test;

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 ScheduledExceutorTest extends TimerTask {

    private String jobName = "";

    public ScheduledExceutorTest(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);
    }
}