线程池

        Executors.newFixedThreadPool(3); //固定数量的线程池   corePoolSize=maximumPoolSize=3
        Executors.newCachedThreadPool(); //缓存线程池corePoolSize =0,maximumPoolSize=Integer.MAX_VALUE,
        Executors.newSingleThreadExecutor();//单线程池 corePoolSize=maximumPoolSize=1
        Executors.newScheduledThreadPool(3); //支持定时或者周期性任务执行
        Executors.newWorkStealingPool(); //支持并行执行任务

    1.如果当前线程池内线程数量小于corePoolSize 数量,会创建一个新的线程，去执行该任务
    2.如果线程内线程数大于corePoolSize,则会将任务 提交到 workQueue(阻塞队列)。通过offer方法添加，会立即返回是否添加成功
    3.如果workQueued队列已经满了，而当前线程池内线程数量小于maximumPoolSize ,
      则创建一个新的线程执行该任务,如果当前线程池内线程数量大于maximumPoolSize数量，则执行拒绝策略
    

public class TestExecute {

    public static void main(String[] args) throws InterruptedException {
        
        LinkedBlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>(5);
        ThreadPoolExecutor threadPool = new ThreadPoolExecutor(5, 10, 3, TimeUnit.SECONDS, queue); // 默认直接抛出异常
        for (int i = 1; i <= 17; i++) {
            Thread.sleep(10);
            threadPool.execute(new Thread(new MyRunnable(), "Thread—Pool-".concat(i + "")));
            System.out.println(" index = "+ i+" ,  线程池的线程数量： " + threadPool.getPoolSize());
            if (queue.size() > 0) {
                System.out.println("----------------任务队列大小" + queue.size());
            }
        }
        threadPool.shutdown();
        System.out.println("*********");
    }

    public static class MyRunnable implements Runnable {
        @Override
        public void run() {
            try {
                //休眠300毫秒
                Thread.sleep(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}