一点一滴-线程池中ScheduledExecutorService定时器功能
使用线程池的好处:
1.减少在创建和销毁线程上所花的时间以及系统资源的开销
2.如不使用线程池，有可能造成系统创建大量线程而导致消耗完系统内存以及”过度切换”。
3.如果在web应用中使用线程，如timer,但是需要设置守护线程，这样在tomcat关闭时，线程也随之关闭。但有些线程不会随着tomcat的关闭而关闭。如：thread 。所以一般需要用线程池统一管理

项目应用的例子
1.线程池执行timer定时任务

         ScheduledExecutorService scheduled_pool = Executors.newScheduledThreadPool(1);Calendar currentDate = Calendar.getInstance();System.out.println(currentDate.getTime());long now =  currentDate.getTime().getTime();currentDate.add(Calendar.SECOND, 10);//Date date = calendar.getTime();long delay = currentDate.getTime().getTime()-now ;long interval = 10*1000;System.out.println(delay);scheduled_pool.scheduleAtFixedRate(new TestTimerRunable(), delay, interval,TimeUnit.MILLISECONDS);

线程池执行thread线程

ScheduledExecutorService scheduled_pool = Executors.newScheduledThreadPool(1);Thread thread = new Thread(new Runnable() {@Override public void run() { // TODO Auto-generated method stub}});thread.setDaemon(true);//线程设置为守护线程 则容器关闭后，这些守护线程会立即关闭scheduled_pool.execute(thread);

2.web应用
1)web.xml中配置监听器,在系统启动时加载线程池

  <listener-class>com.xxx.common.listener.ThreadPoolListener  </listener-class>

2)监听器配置

public class ThreadPoolListener implements ServletContextListener{         public static ScheduledExecutorService scheduled_pool = Executors.newScheduledThreadPool(10);private Logger log = LoggerFactory.getLogger(this.getClass());@Overridepublic void contextDestroyed(ServletContextEvent arg0) {scheduled_pool.shutdown();//关闭线程池 if (!scheduled_pool.isShutdown()) {   try {Thread.currentThread().wait(5000);if (!scheduled_pool.isShutdown()) {scheduled_pool.shutdownNow();//关闭线程池 (强行关闭)}} catch (InterruptedException e) {log.error("关闭所有线程错误",e.getMessage());} finally{if (!scheduled_pool.isShutdown()) {scheduled_pool.shutdownNow();}}}log.info("所有线程关闭"+scheduled_pool.isShutdown());}@Overridepublic void contextInitialized(ServletContextEvent arg0) {}}