使用 ScheduledExecutorService 来替换 Timer

ava.util.Timer计时器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")。

但是，Timer存在一些缺陷：

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;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。 

 测试代码：

 

public class ScheduledExecutorTest {

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

                   final ScheduledExecutorTest test = new ScheduledExecutorTest();

                   // test.lanuchTimer();

                   // Thread.sleep(1000*5);//5秒钟之后添加新任务

                   // test.addOneTask();

                   test.lanuchTimer2();

                   Thread.sleep(1000 * 5);// 5秒钟之后添加一个新任务

                   test.addOneTask2();

         }

 

         private final Timer timer = new Timer();

 

         // 启动计时器

         public void lanuchTimer2() {

                   timer.schedule(new TimerTask() {

                            @Override

                            public void run() {

                                     throw new RuntimeException();

                            }

                   }, 1000 * 3, 500);

         }

 

         // 向计时器添加一个任务

         public void addOneTask2() {

                   timer.schedule(new TimerTask() {

                            @Override

                            public void run() {

                                     System.out.println("hello world");

                            }

                   }, 1000 * 1, 1000 * 5);

         }

 

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

         // TimerTest test = new TimerTest();

         // test.lanuchTimer();

         // Thread.sleep(1000*5);//5秒钟之后添加一个新任务

         // test.addOneTask();

         // }

}

 

 

测试代码结果

Exception in thread "Timer-0" java.lang.RuntimeException

         at com.technology.test.ScheduledExecutorTest$3.run(ScheduledExecutorTest.java:78)

         at java.util.TimerThread.mainLoop(Unknown Source)

         at java.util.TimerThread.run(Unknown Source)

Exception in thread "main" java.lang.IllegalStateException: Timer already cancelled.

         at java.util.Timer.sched(Unknown Source)

         at java.util.Timer.schedule(Unknown Source)

         at com.technology.test.ScheduledExecutorTest.addOneTask2(ScheduledExecutorTest.java:85)

         at com.technology.test.ScheduledExecutorTest.main(ScheduledExecutorTest.java:68)

 

 

那么如果使用ScheduledExecutorService呢？

测试代码如下：

public class ScheduledExecutorTest {

         // 线程池能按时间计划来执行任务，允许用户设定计划执行任务的时间，int类型的参数是设定

         // 线程池中线程的最小数目。当任务较多时，线程池可能会自动创建更多的工作线程来执行任务

         public ScheduledExecutorService scheduExec = Executors

                            .newScheduledThreadPool(1);

 

         // 启动计时器

         public void lanuchTimer() {

                   final Runnable task = new Runnable() {

                            @Override

                            public void run() {

                                     throw new RuntimeException();

                            }

                   };

                   scheduExec.scheduleWithFixedDelay(task, 1000 * 5, 1000 * 10,

                                     TimeUnit.MILLISECONDS);

         }

 

         // 添加新任务

         public void addOneTask() {

                   final Runnable task = new Runnable() {

                            @Override

                            public void run() {

                                     System.out.println("welcome to china");

                            }

                   };

                   scheduExec.scheduleWithFixedDelay(task, 1000 * 1, 1000,

                                     TimeUnit.MILLISECONDS);

         }

 

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

                   final ScheduledExecutorTest test = new ScheduledExecutorTest();

                   // test.lanuchTimer();

                   // Thread.sleep(1000*5);//5秒钟之后添加新任务

                   // test.addOneTask();

 

                   test.lanuchTimer();

                   Thread.sleep(1000 * 5);// 5秒钟之后添加一个新任务

                   test.addOneTask();

         }

 

}