线程池核心线程为0依然执行

    private final ThreadPoolExecutor executorService = new ThreadPoolExecutor(0, 20, 60,
            TimeUnit.MILLISECONDS, new LinkedBlockingQueue<>(1000), new ThreadPoolExecutor.CallerRunsPolicy());

    @GetMapping("/hello")
    public void hello(){
        executorService.execute(()->{
            System.out.println("sleep1");
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println("sleep2");
        });
        System.out.println("hello");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        executorService.execute(()->{
            System.out.println("sleep3");
            System.out.println("sleep4");
        });
    }

　　效果：

hello
sleep1
sleep2
sleep3
sleep4

　　单线程执行