[Java] ThreadPoolExecutor should shutdown after used

Created a ThreadPoolExecutor without shutting it down after used will cause thread leak.

Noncompliant Code

ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) Executors.newFixedThreadPool(1);

threadpool.submit(() -> {
      ...
});

Compilant Code

	ThreadPoolExecutor threadpool = (ThreadPoolExecutor) Executors.newFixedThreadPool(1);
		try {
			threadpool.submit(() -> {
                             ...
                        });

		} finally {
			threadpool.shutdown();
		}

Type : Bug