简单线程池的实现

/**
 * Created by Joker on 2015/3/7.
 */
 public class ThreadPool {
 private static ThreadPool instance = null;
 //空闲的线程队列
 private List<JThread> idleThreads;
 //已有的线程总数
 private int threadCounter = 0;
 private Boolean isShunDown = false;
 public ThreadPool() {
     //初始化空闲线程队列容量为5
     this.idleThreads = new Vector<JThread>(5);
     this.threadCounter = 0;
 }
 private static class SingleTonHolder {
     private static ThreadPool threadPool = new ThreadPool();
 }
 /*单例获得线程池实例*/
 public static ThreadPool getInstance() {
     return SingleTonHolder.threadPool;
 }
 public int getThreadCounter() {
     return threadCounter;
 }

 /**
  * 将线程放入池中，回收线程
  */
 protected synchronized void repool(JThread repoolingThread) {
     if (!isShunDown) {
         idleThreads.add(repoolingThread);
     } else {
         repoolingThread.shutDown();
     }
 }
 /**
  * 停止池中所有线程
  */
 public synchronized void shutDownAll() {
     this.isShunDown = true;
     for (JThread jThread : idleThreads) {
         jThread.shutDown();
     }
 }

 /**
  * 执行线程任务
  */
 public synchronized void execute(Runnable target) {
     this.isShunDown = false;
     JThread jThread = null;
     /*如果池中有空余线程，直接使用该线程*/
     if (idleThreads.size() > 0) {
         jThread = idleThreads.get(idleThreads.size() - 1);
         //将该线程从池中移除
         idleThreads.remove(jThread);
         //立即执行该任务
         jThread.setTarget(target);
     }
     /*没有空闲线程，创建新线程*/
     else {
         threadCounter++;
         //创建线程
         jThread = new JThread(target, "JThread:" + threadCounter, ThreadPool.this);
         jThread.start();
     }
 }
}

/**
 * Created by Joker on 2015/3/7.
 */
 public class JThread extends Thread {
 //线程池
 private ThreadPool threadPool;
 //任务
 private Runnable target;
 private boolean isShutDown = false;
 private boolean isIdle = false;
 public JThread(Runnable target, String name, ThreadPool threadPool) {
     super(name);
     this.target = target;
     this.threadPool = threadPool;
 }
 public Runnable getTarget() {
     return target;
 }
 public boolean isIdle() {
     return isIdle;
 }

 @Override
 public void run() {
     //只要没有关闭，则一直不结束该线程
     while (!isShutDown) {
         isIdle = false;
         if (null != target) {
             //执行任务，注意这里调用的是run()，而不是start()
             target.run();
         }
         //任务结束，闲置状态
         isIdle = true;
         try {
             threadPool.repool(JThread.this);
             synchronized (this) {
                 //线程空闲，等待新的任务到来
                 wait();
             }
         } catch (InterruptedException e) {
         }
         isIdle = false;
     }
 }

 public synchronized void setTarget(Runnable target) {
     this.isShutDown = false;
     this.target = target;
     //设置任务之后，通知run方法，开始执行任务
     notifyAll();
 }

 /**
  * 关闭线程
  */
 public synchronized void shutDown() {
     this.isShutDown = true;
    notifyAll();
 }
}

ThreadPool.getInstance().execute(new Runnable() {
            @Override
            public void run() {
                /*执行任务*/
            }
        });