• 建立一個執行緒池 threadPoolExecutor 執行緒數量為threadCount，
• 執行methodA()方法，threadCount次
• 等待執行緒池的執行緒全部執行完，即latch為0
• shutdown()執行緒池

    @Test
    public void test(int threadCount) {
        ExecutorService threadPoolExecutor = new ThreadPoolExecutor(
　　　　　　　　　 threadCount/2, 
　　　　　　　　　 threadCount,
                1L, TimeUnit.SECONDS,
                
 
new LinkedBlockingQueue<>(threadCount),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());

        CountDownLatch latch = new CountDownLatch(threadCount);

        //迴圈執行methodA()方法
        for (int count = threadCount; count > 0; count--) {
            threadPoolExecutor.submit(() 
 
-> {
                try {
                    methodA( );
                } catch (Exception e) {
                    log.error(e.getMessage(), e);
                } finally {
                    latch.countDown();
                }
            });
        }

        //阻塞當前主執行緒，直到latch等於0
        try
 
 {
            //阻塞當前執行緒，直到計數器的值為0
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //關閉執行緒池
        threadPoolExecutor.shutdown();
    }