code: public static String get(String subPath) {
          String dataStr = null;
          try {
              dataStr = loadingCache.get(subPath).snd;
          } catch (ExecutionException e) {
              LOG.error(e);
          }
          return dataStr;
      }
docs: 如果本地缓存未命中那么从远程找,是经典的"if cached, return; otherwise create, cache and return" pattern