shutdown方法

1.线程池状态变为shutdown

2.不会接收新任务

3.已提交的任务会执行完

4.此方法不会阻塞调用线程执行

ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.submit(() -> {
           log.debug("task1 running");
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            log.debug("task1 finished");
        });
        executorService.submit(() -> {
            log.debug("task2 running");
            try {
                TimeUnit.SECONDS.sleep(1);