几种任务调度的 Java 实现方法与比较

约定不等于承诺〃 2022-05-16 03:24 195阅读 0赞

综观目前的 Web 应用，多数应用都具备任务调度的功能。本文由浅入深介绍了几种任务调度的 Java 实现方法，包括 Timer，Scheduler, Quartz 以及 JCron Tab，并对其优缺点进行比较，目的在于给需要开发任务调度的程序员提供有价值的参考。

前言

任务调度是指基于给定时间点，给定时间间隔或者给定执行次数自动执行任务。本文由浅入深介绍四种任务调度的 Java 实现：

*  Timer
 *  ScheduledExecutor
 *  开源工具包 Quartz
 *  开源工具包 JCronTab

此外，为结合实现复杂的任务调度，本文还将介绍 Calendar 的一些使用方法。

Timer

相信大家都已经非常熟悉 java.util.Timer 了，它是最简单的一种实现任务调度的方法，下面给出一个具体的例子：

使用 Timer 实现任务调度的核心类是 Timer 和 TimerTask。其中 Timer 负责设定 TimerTask 的起始与间隔执行时间。使用者只需要创建一个 TimerTask 的继承类，实现自己的 run 方法，然后将其丢给 Timer 去执行即可。

Timer 的设计核心是一个 TaskList 和一个 TaskThread。Timer 将接收到的任务丢到自己的 TaskList 中，TaskList 按照 Task 的最初执行时间进行排序。TimerThread 在创建 Timer 时会启动成为一个守护线程。这个线程会轮询所有任务，找到一个最近要执行的任务，然后休眠，当到达最近要执行任务的开始时间点，TimerThread 被唤醒并执行该任务。之后 TimerThread 更新最近一个要执行的任务，继续休眠。

Timer 的优点在于简单易用，但由于所有任务都是由同一个线程来调度，因此所有任务都是串行执行的，同一时间只能有一个任务在执行，前一个任务的延迟或异常都将会影响到之后的任务。

ScheduledExecutor

鉴于 Timer 的上述缺陷，Java 5 推出了基于线程池设计的 ScheduledExecutor。其设计思想是，每一个被调度的任务都会由线程池中一个线程去执行，因此任务是并发执行的，相互之间不会受到干扰。需 要注意的是，只有当任务的执行时间到来时，ScheduedExecutor 才会真正启动一个线程，其余时间 ScheduledExecutor 都是在轮询任务的状态。

上面代码展示了 ScheduledExecutorService 中两种最常用的调度方法 ScheduleAtFixedRate 和 ScheduleWithFixedDelay。ScheduleAtFixedRate 每次执行时间为上一次任务开始起向后推一个时间间隔，即每次执行时间为 :initialDelay, initialDelay+period, initialDelay+2\*period, …；ScheduleWithFixedDelay 每次执行时间为上一次任务结束起向后推一个时间间隔，即每次执行时间为：initialDelay, initialDelay+executeTime+delay, initialDelay+2\*executeTime+2\*delay。由此可见，ScheduleAtFixedRate 是基于固定时间间隔进行任务调度，ScheduleWithFixedDelay 取决于每次任务执行的时间长短，是基于不固定时间间隔进行任务调度。

用 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。

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">087</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">.getEarliestDate(currentDate,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">3</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">16</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">38</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">10</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">);</code></td> 
  </tr> 
 </tbody> 
</table>

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">094</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">long</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">period =&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">7</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">24</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">1000</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">;</code></td> 
  </tr> 
 </tbody> 
</table>

清单 3 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：

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。

可以看出，用上述方法实现该任务调度比较麻烦，这就需要一个更加完善的任务调度框架来解决这些复杂的调度问题。幸运的是，开源工具包 Quartz 与 JCronTab 提供了这方面强大的支持。

Quartz

Quartz 可以满足更多更复杂的调度需求，首先让我们看看如何用 Quartz 实现每星期二 16:38 的调度安排：

清单 4 非常简洁地实现了一个上述复杂的任务调度。Quartz 设计的核心类包括 Scheduler, Job 以及 Trigger。其中，Job 负责定义需要执行的任务，Trigger 负责设置调度策略，Scheduler 将二者组装在一起，并触发任务开始执行。

Job

使用者只需要创建一个 Job 的继承类，实现 execute 方法。JobDetail 负责封装 Job 以及 Job 的属性，并将其提供给 Scheduler 作为参数。每次 Scheduler 执行任务时，首先会创建一个 Job 的实例，然后再调用 execute 方法执行。Quartz 没有为 Job 设计带参数的构造函数，因此需要通过额外的 JobDataMap 来存储 Job 的属性。JobDataMap 可以存储任意数量的 Key，Value 对，例如：

JobDataMap 中的数据可以通过下面的方式获取：

Trigger

Trigger 的作用是设置调度策略。Quartz 设计了多种类型的 Trigger，其中最常用的是 SimpleTrigger 和 CronTrigger。

SimpleTrigger 适用于在某一特定的时间执行一次，或者在某一特定的时间以某一特定时间间隔执行多次。上述功能决定了 SimpleTrigger 的参数包括 start-time, end-time, repeat count, 以及 repeat interval。

Repeat count 取值为大于或等于零的整数，或者常量 SimpleTrigger.REPEAT\_INDEFINITELY。

Repeat interval 取值为大于或等于零的长整型。当 Repeat interval 取值为零并且 Repeat count 取值大于零时，将会触发任务的并发执行。

Start-time 与 dnd-time 取值为 java.util.Date。当同时指定 end-time 与 repeat count 时，优先考虑 end-time。一般地，可以指定 end-time，并设定 repeat count 为 REPEAT\_INDEFINITELY。

以下是 SimpleTrigger 的构造方法：

举例如下：

创建一个立即执行且仅执行一次的 SimpleTrigger：

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">2</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">new</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">SimpleTrigger(</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:blue!important; white-space:nowrap">"myTrigger"</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:blue!important; white-space:nowrap">"myGroup"</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">new</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">Date(),&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">null</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">0</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">, 0L);</code></td> 
  </tr> 
 </tbody> 
</table>

创建一个半分钟后开始执行，且每隔一分钟重复执行一次的 SimpleTrigger：

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">3</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">new</code>&nbsp;<code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">Date(System.currentTimeMillis()+</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">30</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">1000</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">),&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">null</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">0</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">1000</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">);</code></td> 
  </tr> 
 </tbody> 
</table>

创建一个 2011 年 6 月 1 日 8:30 开始执行，每隔一小时执行一次，一共执行一百次，一天之后截止的 SimpleTrigger：

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">10</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">Date endTime =&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:bold!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,102,153)!important; white-space:nowrap">new</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">Date (calendar.getTimeInMillis() +</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">24</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">1000</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">);</code></td> 
  </tr> 
 </tbody> 
</table>

<table style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; text-align:left!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important; border-collapse:collapse!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:10pt!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; border:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(175,175,175)!important"> <code style="padding-top:0px; padding-right:0.3em!important; padding-bottom:0px; padding-left:5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap; display:block!important">12</code></td> 
   <td style="padding:0px 0px 0px 0.5em!important; margin:0px!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important"> <code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:blue!important; white-space:nowrap">"myGroup"</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">, startTime, endTime,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">100</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">,&nbsp;</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">60</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">*</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; color:rgb(0,153,0)!important; white-space:nowrap">1000</code><code style="padding:0px 5px; margin:0px 2px; border:1px solid rgb(221,221,221); outline:0px!important; background-color:rgb(246,246,246); float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:10pt!important; min-height:inherit!important; white-space:nowrap">);</code></td> 
  </tr> 
 </tbody> 
</table>

上述最后一个例子中，同时设置了 end-time 与 repeat count，则优先考虑 end-time，总共可以执行二十四次。

CronTrigger 的用途更广，相比基于特定时间间隔进行调度安排的 SimpleTrigger，CronTrigger 主要适用于基于日历的调度安排。例如：每星期二的 16:38:10 执行，每月一号执行，以及更复杂的调度安排等。

CronTrigger 同样需要指定 start-time 和 end-time，其核心在于 Cron 表达式，由七个字段组成：

举例如下：

创建一个每三小时执行的 CronTrigger，且从每小时的整点开始执行：

创建一个每十分钟执行的 CronTrigger，且从每小时的第三分钟开始执行：

创建一个每周一，周二，周三，周六的晚上 20:00 到 23:00，每半小时执行一次的 CronTrigger：

创建一个每月最后一个周四，中午 11:30-14:30，每小时执行一次的 trigger：

解释一下上述例子中各符号的含义：

首先所有字段都有自己特定的取值，例如，Seconds 和 Minutes 取值为 0 到 59，Hours 取值为 0 到 23，Day-of-Month 取值为 0-31, Month 取值为 0-11，或者 JAN，FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC，Days-of-Week 取值为 1-7 或者 SUN, MON, TUE, WED, THU, FRI, SAT。每个字段可以取单个值，多个值，或一个范围，例如 Day-of-Week 可取值为“MON，TUE，SAT”,“MON-FRI”或者“TUE-THU，SUN”。

通配符 \* 表示该字段可接受任何可能取值。例如 Month 字段赋值 \* 表示每个月，Day-of-Week 字段赋值 \* 表示一周的每天。

/ 表示开始时刻与间隔时段。例如 Minutes 字段赋值 2/10 表示在一个小时内每 20 分钟执行一次，从第 2 分钟开始。

? 仅适用于 Day-of-Month 和 Day-of-Week。? 表示对该字段不指定特定值。适用于需要对这两个字段中的其中一个指定值，而对另一个不指定值的情况。一般情况下，这两个字段只需对一个赋值。

L 仅适用于 Day-of-Month 和 Day-of-Week。L 用于 Day-of-Month 表示该月最后一天。L 单独用于 Day-of-Week 表示周六，否则表示一个月最后一个星期几，例如 5L 或者 THUL 表示该月最后一个星期四。

W 仅适用于 Day-of-Month，表示离指定日期最近的一个工作日，例如 Day-of-Month 赋值为 10W 表示该月离 10 号最近的一个工作日。

\# 仅适用于 Day-of-Week，表示该月第 XXX 个星期几。例如 Day-of-Week 赋值为 5\#2 或者 THU\#2，表示该月第二个星期四。

CronTrigger 的使用如下：

Job 与 Trigger 的松耦合设计是 Quartz 的一大特点，其优点在于同一个 Job 可以绑定多个不同的 Trigger，同一个 Trigger 也可以调度多个 Job，灵活性很强。

Listener

除了上述基本的调度功能，Quartz 还提供了 listener 的功能。主要包含三种 listener：JobListener，TriggerListener 以及 SchedulerListener。当系统发生故障，相关人员需要被通知时，Listener 便能发挥它的作用。最常见的情况是，当任务被执行时，系统发生故障，Listener 监听到错误，立即发送邮件给管理员。下面给出 JobListener 的实例：

清单 7. JobListener 的实现

public class MyListener implements JobListener{

@Override
	public String getName() {
		return "My Listener";
	}
	@Override
	public void jobWasExecuted(JobExecutionContext context,
			JobExecutionException jobException) {
		if(jobException != null){
			try {
				//停止Scheduler
				context.getScheduler().shutdown();
				System.out.println("
                Error occurs when executing jobs, shut down the scheduler ");
                // 给管理员发送邮件…
			} catch (SchedulerException e) {
				e.printStackTrace();
			}
		}
	}
}</pre> </td> 
  </tr> 
 </tbody> 
</table>

从清单 7 可以看出，使用者只需要创建一个 JobListener 的继承类，重载需要触发的方法即可。当然，需要将 listener 的实现类注册到 Scheduler 和 JobDetail 中：

使用者也可以将 listener 注册为全局 listener，这样便可以监听 scheduler 中注册的所有任务 :

为了测试 listener 的功能，可以在 job 的 execute 方法中强制抛出异常。清单 7 中，listener 接收到异常，将 job 所在的 scheduler 停掉，阻止后续的 job 继续执行。scheduler、jobDetail 等信息都可以从 listener 的参数 context 中检索到。

清单 7 的输出结果为：

<table style="padding:0px; margin:0px; font-family:微软雅黑,Verdana,sans-serif,宋体; color:rgb(0,0,0); font-size:14px; line-height:22px; text-align:left; background-color:rgb(249,249,249)"> 
 <tbody style="padding:0px; margin:0px"> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:0px; margin:0px"> <pre style="padding:5px; margin-top:10px; margin-bottom:10px; font-size:9pt; font-family:'Courier New',Arial; border-width:1px 1px 1px 5px; border-style:solid; border-color:rgb(221,221,221) rgb(221,221,221) rgb(221,221,221) rgb(108,226,108); background-color:rgb(246,246,246)"> Generating report - myJob.myJob, type =FULL 
 Tue Feb 15 18:57:35 CST 2011 
 2011-2-15 18:57:35 org.quartz.core.JobRunShell run 
信息 : Job myJob.myJob threw a JobExecutionException: 
 org.quartz.JobExecutionException 
 at com.ibm.scheduler.QuartzListenerTest.execute(QuartzListenerTest.java:22) 
 at org.quartz.core.JobRunShell.run(JobRunShell.java:191) 
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516) 
 2011-2-15 18:57:35 org.quartz.core.QuartzScheduler shutdown 
信息 : Scheduler DefaultQuartzScheduler_$_NON_CLUSTERED shutting down. 
 Error occurs when executing jobs, shut down the scheduler </pre> </td> 
  </tr> 
 </tbody> 
</table>

TriggerListener、SchedulerListener 与 JobListener 有类似的功能，只是各自触发的事件不同，如 JobListener 触发的事件为：

Job to be executed, Job has completed execution 等

TriggerListener 触发的事件为：

Trigger firings, trigger mis-firings, trigger completions 等

SchedulerListener 触发的事件为：

add a job/trigger, remove a job/trigger, shutdown a scheduler 等

读者可以根据自己的需求重载相应的事件。

JobStores

Quartz 的另一显著优点在于持久化，即将任务调度的相关数据保存下来。这样，当系统重启后，任务被调度的状态依然存在于系统中，不会丢失。默认情况 下，Quartz 采用的是 org.quartz.simpl.RAMJobStore，在这种情况下，数据仅能保存在内存中，系统重启后会全部丢失。若想持久化数据，需要采用 org.quartz.simpl.JDBCJobStoreTX。

实现持久化的第一步，是要创建 Quartz 持久化所需要的表格。在 Quartz 的发布包 docs/dbTables 中可以找到相应的表格创建脚本。Quartz 支持目前大部分流行的数据库。本文以 DB2 为例，所需要的脚本为 tables\_db2.sql。首先需要对脚本做一点小的修改，即在开头指明 Schema：

为了方便重复使用 , 创建表格前首先删除之前的表格：  
`drop table qrtz_job_details;`

…

然后创建数据库 sched，执行 tables\_db2.sql 创建持久化所需要的表格。

第二步，配置数据源。数据源与其它所有配置，例如 ThreadPool，均放在 quartz.properties 里：

清单 8. Quartz 配置文件

# Configure Datasources 
 org.quartz.jobStore.class = org.quartz.impl.jdbcjobstore.JobStoreTX 
 org.quartz.jobStore.driverDelegateClass = org.quartz.impl.jdbcjobstore.StdJDBCDelegate 
 org.quartz.jobStore.dataSource = db2DS 
 org.quartz.jobStore.tablePrefix = QRTZ_

org.quartz.dataSource.db2DS.driver = com.ibm.db2.jcc.DB2Driver 
 org.quartz.dataSource.db2DS.URL = jdbc:db2://localhost:50001/sched 
 org.quartz.dataSource.db2DS.user = quartz 
 org.quartz.dataSource.db2DS.password = passw0rd 
 org.quartz.dataSource.db2DS.maxConnections = 5 </pre> </td> 
  </tr> 
 </tbody> 
</table>

使用时只需要将 quatz.properties 放在 classpath 下面，不用更改一行代码，再次运行之前的任务调度实例，trigger、job 等信息便会被记录在数据库中。

将清单 4 中的 makeWeeklyTrigger 改成 makeSecondlyTrigger，重新运行 main 函数，在 sched 数据库中查询表 qrtz\_simple\_triggers 中的数据。其查询语句为“db2 ‘ select repeat\_interval, times\_triggered from qrtz\_simple\_triggers ’”。结果 repeat\_interval 为 1000，与程序中设置的 makeSecondlyTrigger 相吻合，times\_triggered 值为 21。

停掉程序，将数据库中记录的任务调度数据重新导入程序运行：

JCronTab

习惯使用 unix/linux 的开发人员应该对 crontab 都不陌生。Crontab 是一个非常方便的用于 unix/linux 系统的任务调度命令。JCronTab 则是一款完全按照 crontab 语法编写的 java 任务调度工具。

首先简单介绍一下 crontab 的语法，与上面介绍的 Quartz 非常相似，但更加简洁 , 集中了最常用的语法。主要由六个字段组成（括弧中标识了每个字段的取值范围）：

与 Quartz 相比，省略了 Seconds 与 Year，多了一个 command 字段，即为将要被调度的命令。JCronTab 中也包含符号“\*”与“/”, 其含义与 Quartz 相同。

举例如下：

每天 12 点到 15 点 , 每隔 1 小时执行一次 Date 命令：

每月 2 号凌晨 1 点发一封信给 zhjingbj@cn.ibm.com：

每周一，周二，周三，周六的晚上 20:00 到 23:00，每半小时打印“normal”：

JCronTab 借鉴了 crontab 的语法，其区别在于 command 不再是 unix/linux 的命令，而是一个 Java 类。如果该类带参数，例如“com.ibm.scheduler.JCronTask2\#run”，则定期执行 run 方法；如果该类不带参数，则默认执行 main 方法。此外，还可以传参数给 main 方法或者构造函数，例如“com.ibm.scheduler.JCronTask2\#run Hello World“表示传两个参数 Hello 和 World 给构造函数。

JCronTab 与 Quartz 相比，其优点在于，第一，支持多种任务调度的持久化方法，包括普通文件、数据库以及 XML 文件进行持久化；第二，JCronTab 能够非常方便地与 Web 应用服务器相结合，任务调度可以随 Web 应用服务器的启动自动启动；第三，JCronTab 还内置了发邮件功能，可以将任务执行结果方便地发送给需要被通知的人。

JCronTab 与 Web 应用服务器的结合非常简单，只需要在 Web 应用程序的 web.xml 中添加如下行：

接下来，需要撰写 D:/Scheduler/src/jcrontab.properties 的内容，其内容根据需求的不同而改变。

当采用普通文件持久化时，jcrontab.properties 的内容主要包括：

其中数据来源 org.jcrontab.data.datasource 被描述为普通文件，即 org.jcrontab.data.FileSource。具体的文件即 org.jcrontab.data.file 指明为 D:/Scheduler/src/crontab。

Crontab 描述了任务的调度安排：

其中包含了两条任务的调度，分别是每两分钟执行一次 JCronTask1 的 main 方法，每一分钟执行一次 JCronTask2 的 run 方法。

<table style="padding:0px; margin:0px; font-family:微软雅黑,Verdana,sans-serif,宋体; color:rgb(0,0,0); font-size:14px; line-height:22px; text-align:left; background-color:rgb(249,249,249)"> 
 <tbody style="padding:0px; margin:0px"> 
  <tr style="padding:0px; margin:0px"> 
   <td style="padding:0px; margin:0px"> <pre style="padding:5px; margin-top:10px; margin-bottom:10px; font-size:9pt; font-family:'Courier New',Arial; border-width:1px 1px 1px 5px; border-style:solid; border-color:rgb(221,221,221) rgb(221,221,221) rgb(221,221,221) rgb(108,226,108); background-color:rgb(246,246,246)"> --------------Task2----------------- 
 Current Time = Tue Feb 15 09:22:00 CST 2011, Count = 0 
 enter into run method 
 This is arg 0 Hello 
 This is arg 1 World 
 --------------Task1----------------- 
 Current Time = Tue Feb 15 09:22:00 CST 2011, Count = 0 
 --------------Task2----------------- 
 Current Time = Tue Feb 15 09:23:00 CST 2011, Count = 1 
 enter into run method 
 This is arg 0 Hello 
 This is arg 1 World 
 --------------Task2----------------- 
 Current Time = Tue Feb 15 09:24:00 CST 2011, Count = 2 
 enter into run method 
 This is arg 0 Hello 
 This is arg 1 World 
 --------------Task1----------------- 
 Current Time = Tue Feb 15 09:24:00 CST 2011, Count = 1 </pre> </td> 
  </tr> 
 </tbody> 
</table>

通过修改 jcrontab.properties 中 datasource，可以选择采用数据库或 xml 文件持久化，感兴趣的读者可以参考 [进阶学习 JCronTab][JCronTab]。

此外，JCronTab 还内置了发邮件功能，可以将任务执行结果方便地发送给需要被通知的人。其配置非常简单，只需要在 jcontab.properties 中添加几行配置即可：

结束语

本文介绍了四种常用的对任务进行调度的 Java 实现方法，即 Timer，ScheduledExecutor, Quartz 以及 JCronTab。文本对每种方法都进行了实例解释，并对其优缺点进行比较。对于简单的基于起始时间点与时间间隔的任务调度，使用 Timer 就足够了；如果需要同时调度多个任务，基于线程池的 ScheduledTimer 是更为合适的选择；当任务调度的策略复杂到难以凭借起始时间点与时间间隔来描述时，Quartz 与 JCronTab 则体现出它们的优势。熟悉 Unix/Linux 的开发人员更倾向于 JCronTab，且 JCronTab 更适合与 Web 应用服务器相结合。Quartz 的 Trigger 与 Job 松耦合设计使其更适用于 Job 与 Trigger 的多对多应用场景。

[JCronTab]: http://blog.csdn.net/maskice/archive/2007/06/28/1670070.aspx