线程池的使用

ExecutorService executorService = Executors.newCachedThreadPool();

   public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }
     Integer.MAX_VALUE 容易OOM

/**
 * 如果是CPU密集型，CPU用的高，maximumPoolSize = CPU核数+1
 *
 */
//获取电脑线程数
System.out.println(Runtime.getRuntime().availableProcessors());
ExecutorService executorService = new ThreadPoolExecutor(
        2,//核心线程数
        5,//最大线程数
        2L,//等待时间
        TimeUnit.SECONDS,,//等待时间的单位
        new LinkedBlockingQueue<>(3),//等待的阻塞消息队列
        Executors.defaultThreadFactory(),//使用默认工厂创建
        /**
         * 拒绝策略
         * .AbortPolicy()默认的 ，拒绝执行策略
         * CallerRunsPolicy(),该策略不会抛弃任务，也不会爆出异常，将任务会退给调用者
         * DiscardPolicy()，多余丢失不报错
         * DiscardOldestPolicy 丢掉最老的
         */
       // new ThreadPoolExecutor.AbortPolicy());
       // new ThreadPoolExecutor.CallerRunsPolicy());
      //  new ThreadPoolExecutor.DiscardPolicy());
        new ThreadPoolExecutor.DiscardOldestPolicy());//拒绝策略