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); } }