线程池（3）Executors.newCachedThreadPool

例子：

ExecutorService es = Executors.newCachedThreadPool();
        try {
            for (int i = 0; i < 20; i++) {
                Runnable syncRunnable = new Runnable() {
                    @Override
                    public void run() {
                        log.info(Thread.currentThread().getName());
                        try {
                            Thread.sleep(2000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                };
                es.execute(syncRunnable);
            }
        } finally {
            es.shutdown();
        }

运行结果：

            10:21:04.610 pool-1-thread-13
            10:21:04.612 pool-1-thread-3
            10:21:04.612 pool-1-thread-7
            10:21:04.612 pool-1-thread-2
            10:21:04.610 pool-1-thread-14
            10:21:04.612 pool-1-thread-6
            10:21:04.611 pool-1-thread-8
            10:21:04.611 pool-1-thread-11
            10:21:04.611 pool-1-thread-4
            10:21:04.610 pool-1-thread-1
            10:21:04.611 pool-1-thread-20
            10:21:04.611 pool-1-thread-12
            10:21:04.610 pool-1-thread-16
            10:21:04.611 pool-1-thread-5
            10:21:04.611 pool-1-thread-9
            10:21:04.610 pool-1-thread-17
            10:21:04.610 pool-1-thread-18
            10:21:04.610 pool-1-thread-10
            10:21:04.611 pool-1-thread-15
            10:21:04.611 pool-1-thread-19

调用的调用的ThreadPoolExecutor：

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

corePoolSize=0，maximumPoolSize=Integer.MAX_VALUE

keepAliveTime=60秒

allowCoreThreadTimeout=false（默认）

因此，

• 核心线程数为0
• 每来一个任务，先查看缓冲池中是否有可用线程（没超过60秒的），如果有，则用；没有，则就创建一个新线程
• 因为核心线程数为0，池中的线程当达到60秒时，会超时关闭，直到核心线程数=0