SpringBootTest多线程报错的根本原因(dataSourcealreadyclosed)

@Component
public class EventListener implements ApplicationListener<ApplicationEvent> {

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ContextClosedEvent) {
            LoggerClient.info("容器即将关闭");
            //线程池工具类
            ThreadPoolUtil threadPoolUtil = new ThreadPoolUtil();
            while (threadPoolUtil.getExecutor().isTerminated()) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

​public class ThreadPoolUtil {
    private static final ExecutorService executor = Executors.newFixedThreadPool(20);
    public ThreadPoolUtil() {
    }
    public ExecutorService getExecutor() {
        return executor;
    }
    public static void submitRunnable(Runnable runnable) {
        executor.submit(runnable);
    }
    public static <V> Future submitCallable(Callable<V> callable) {
        Future<V> submit = executor.submit(callable);
        return submit;
    }
}