utorService取代Timer.doc

Java并发编程实战一书提到的用ExecutorService取代Java Timer有几个理由，我认为其中最重要的理由是： 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。这种情况下，Timer也不会再重新恢复线程的执行了;它错误的认为整个Timer都被取消了。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。 stackoverflow上也有关于此问题的讨论： /questions/409932/java-timer-vs-executorservice Timer的问题： Java代码 1 package com.ljn.timer; 2 3 import java.util.Date; 4 import java.util.Timer; 5 6 /* 7 * author lijinnan 8 * date:2013-11-25 下午3:27:43 9 */ 10 public class TimerException 11 12 public static void main(String args) 13 System.out.println(start: + new Date(); 14 Timer timer = new Timer(); 15 int delay = 1000; 16 int period = 2000; 17 timer.schedule(new OKTask(), delay * 2, period); /OKTask does not get chance to execute 18 timer.schedule(new ErrorTask(), delay, period); /exception in ErrorTask will terminate the Timer 19 20 21 /*输出： 22 start:Mon Nov 25 17:49:53 CST 2013 23 ErrorTask is executing. 24 error:Mon Nov 25 17:49:55 CST 2013 25 Exception in thread Timer-0 java.lang.RuntimeException: something wrong 26 at com.ljn.timer.ErrorTask.run(ErrorTask.java:14) 27 */ 28 29 用ExecutorService则正常： Java代码 30 package com.ljn.timer; 31 32 import java.util.Date; 33 import java.util.concurrent.Executors; 34 import java.util.concurrent.ScheduledExecutorService; 35 import java.util.concurrent.TimeUnit; 36 37 /* 38 * author lijinnan 39 * date:2013-11-25 下午3:35:39 40 */ 41 public class ScheduledExecutorServiceTest 42 43 public static ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(2); 44 45 public static void main(String args) 46 System.out.println(start: + new Date(); 47 ErrorTask errorTask = new ErrorTask(); 48 OKTask okTask = new OKTask(); 49 int delay = 1000; 50 int period = 2000; 51 scheduledExecutorService.scheduleAtFixedRate(errorTask, delay, period, TimeUnit.MILLISECONDS); /ErrorTask throws Exception and then stopes. 52 scheduledExecutorService.scheduleAtFixedRate(okTask, delay * 2, period, TimeUnit.MILLISECONDS); /OKTask is executed periodically, not affected by ErrorTask 53 54 /scheduledExecutorService.shutdown(); 55 56 57 /* 58 start:Mon Nov 25 17:54:22 CST 2013 59 ErrorTask is executing. 60 error occurs:Mon Nov 25 17:54:24 CST 2013 61 OKTask is executed:Mon Nov 25 17:54:24 CST 2013 62 OKTask is executed:Mon Nov 25 17:54:26 CST 2013 63 OKTask is executed:Mon Nov 25 17:54:28 CST 2013 64 . 65 */ 66 67 另外开发中常常会让任务在每天的指定时间点运行，示例如下： Java代码 68 package com.ljn.timer; 69 70 import java.util.Date; 71 import java.util.concurrent.Executors; 72 import java.util.concurrent.ScheduledExecutorService; 73 import java.util.concurrent.TimeUnit; 74 75 /* 76 * author lijinnan 77 * date:2013-11-25 下午5:18:55 78 */ 79 public class FixedDatetimeTaskTest 80 81 public static ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1); 82 83 public static void main(String args) throws Exception 84 System.out.println(start: + new Date(); 85 86 /每天的02:30:00执行任务 87 long delay = Helper.calcDelay(2, 30, 0); 88 long period = Helper.ONE_DAY; 89 scheduledExecutorService.scheduleAtFixedRate(new OKTask(), delay, period, TimeUnit.MILLISECONDS); 90 91 92 文章中用到的其他类： Java代码 93 package com.ljn.timer; 94 95 import java.util.Date; 96 import java.util.TimerTask; 97 98 public class ErrorTask extends TimerTask 99 100 Override 101 public void run() 102 try 103 System.out.println(ErrorTask is executing.); 104 Thread.sleep(1000); 105 System.out.println(error occurs: + new Date(); 106 throw new RuntimeException(something wrong); 107 catch (InterruptedException e) 108 109 110 111 Java代码 112 package com.ljn.timer; 113 114 import java.util.Date; 115 import java.util.TimerTask; 116 117 118 public class OKTask extends TimerTask 119 120 Override 121 public void run() 122 System.out.println(OKTask is executed: + new Date(); 123 124 Java代码 125 package com.ljn.timer; 126 127 import org.joda.time.DateTime; 128 129 /* 130 * author lijinnan 131 * date:2013-11-25 下午5:17:40 132 */ 133 public class Helper 134 135 private Helper() 136 137 public static final long ONE_DAY = 60 * 60 * 24; 138 139 public static long calcDelay(int hour, int minute, int second) 140 if (!(0 = hour & hour =23 & 0 = minute & minute =59 & 0 =second & second = 59) 141 throw new IllegalArgumentException(); 142 143 return calcDelay(fixed(hour, minute, second); 144 145 146 private static long calcDelay(DateTime targetDatetimeOfToday) 147 long delay = 0; 148 DateTime now = new DateTime(); 149 150 /时间点已过，只好延时到明天的这个时间点再执行 151 if (now.isAfter(targetDatetimeOfToday) 152 delay = now.plusDays(1).getMillis() - now.getMillis(); 153 154 /时间点未到 155 else 156 delay = targetDatetimeOfToday.getMillis() - now.getMillis(); 157 158 159 return delay; 160 161 162 /* 163 * 返回这样一个DateTime对象： 164 * 1.日期为今天 165 * 2.时分秒为参数指定的值 166 * param hour 0-23 167