java在for循环中使用concurrent包进行多线程编程

  最近在做接口的时候总是遇到一个for语句中 每次循环会涉及很多资源,包括 ftp io db,总想用现场来控制太.找到一篇文章  http://daoger.javaeye.com/blog/142485 写的不错.自己写了2个demo
1. 主线程不等待
 public class CopyOfTestThreadPool {
 public static void main(String args[]) throws InterruptedException {
  // only two threads
  ExecutorService exec = Executors.newFixedThreadPool(20);
  List<Long> list = new ArrayList<Long>();
  for(int index = 0; index < 1000000; index++){
   list.add(System.nanoTime());
  }
  
  long start = System.currentTimeMillis();
  for (Long long1 : list) {
   final Long l = long1;
   exec.execute(new Runnable(){
    public void run() {
     System.out.println(l);
     try {
      Thread.sleep(5000);
     } catch (InterruptedException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
     
    }});
  }
  // must shutdown
  exec.shutdown();
   long end = System.currentTimeMillis();
   System.out.print("共计用时 ");
   System.out.println(end  - start);
 }
}
2 主线程会等待
public class TestCountDownLatch {
 public static void main(String[] args) throws InterruptedException {
  long start = System.currentTimeMillis();
  // 开始的倒数锁
  final CountDownLatch begin = new CountDownLatch(1);
  // 结束的倒数锁
  final CountDownLatch end = new CountDownLatch(10000);
  // 十名选手
  final ExecutorService exec = Executors.newFixedThrea