code: public synchronized static ExecutorService getExecutorService() {
          if (executorService == null) {
              executorService = Executors.newCachedThreadPool();
              ((ThreadPoolExecutor) executorService).setMaximumPoolSize(executorPoolSize);
          }
          return executorService;
      }
docs: Gets the default {@link ExecutorService} instance, which is a cached thread pool.
  
  @return The default {@link ExecutorService}.