import java.util.Iterator; import java.util.LinkedList; import java.util.Set; import java.util.TreeSet;

public class ThreadPool extends ThreadGroup {

 private LinkedList<Runnable> workQueue = null; // 工作队列

 private static int coreActiveSize = 1;//核心线程个数

 private static int maxActiveSize = 5;//允许最大线程个数

 private static ThreadPool threadPool;//单例

 Set<Integer> threadIdSet = new TreeSet<Integer>();//有序线程队列

 /**

  * private constructor   *   * @param poolSize   */  private ThreadPool() { // poolSize   // 表示线程池中的工作线程的数量   super("AllReportPool"); // 指定ThreadGroup的名称   if (coreActiveSize <= 0 || maxActiveSize <= 0) {    throw new IllegalArgumentException(      "Thread Pool active size should be much more than 0");   }   if (coreActiveSize > maxActiveSize) {    throw new IllegalArgumentException(      "Thread Pool max active size should be much more than core active size");   }   setDaemon(false); // 继承到的方法，设置是否守护线程池   workQueue = new LinkedList<Runnable>(); // 创建工作队列   // 创建并启动工作线程,核心线程池数量是多少就创建多少个工作线程实例   // 设置线程池中允许创建的线程的最大数量   for (int i = 1; i <= maxActiveSize; i++) {    threadIdSet.add(i);   }  }

 /**

  * this method used to create a single instance for this Class   *   * @return instance   */  public static ThreadPool getSingleInstance() {   if (null == threadPool) {    threadPool = new ThreadPool();   }   return threadPool;  }

 /** 向工作队列中加入一个新任务,由工作线程去执行该任务 */

 public synchronized void execute(Runnable task) {   if (task != null) {    workQueue.addLast(task);// 向队列中加入一个任务

   Iterator<Integer> iter = threadIdSet.iterator();

   if (null != iter && iter.hasNext()) {     Integer id = iter.next();     if (this.activeCount() < maxActiveSize) {      threadIdSet.remove(id);      printLog("create new work thread " + id);      new WorkThread(id).start();     }    }    notify(); // 唤醒一个正在getTask()方法中待任务的工作线程   }  }

 /**

  * this method used to print run time message when export all report   * @param msg print message   */  private void printLog(String msg) {   //System.out.println(msg);  }

 /**

  * 内部类,工作线程,负责从工作队列中取出任务,并执行   *   * @author sunnylocus   */  private class WorkThread extends Thread {   private int id;

  public WorkThread(int id) {

   // 父类构造方法,将线程加入到当前ThreadPool线程组中    super(ThreadPool.this, "Work Thread " + id);    this.id = id;   }

  /** 从工作队列中取出一个任务,工作线程会调用此方法,并执行该任务 */

  public void run() {    while (!isInterrupted()) { // isInterrupted()方法继承自Thread类，判断线程是否被中断     Runnable task = null;     // 必须同步工作队列     synchronized (workQueue) {      while (workQueue.size() == 0) {       // destory this active thread       printLog("no task in the queue, close work thread" + id);       threadIdSet.add(id);       return;      }

     task = workQueue.removeFirst(); // 反回队列中第一个元素,并从队列中删除

    }     // 如果getTask()返回null或者线程执行getTask()时被中断，则结束此线程     if (task == null || isInterrupted()) {      return;     }     try {      printLog("work thread " + id + " begin task...");      task.run(); // 运行任务     } catch (Throwable t) {      t.printStackTrace();     }

   }// end while

  }// end run  }// end workThread }  

 

 

用法：

  ThreadPool threadPool = ThreadPool.getSingleInstance();

  threadPool.execute(one tread instance);