docs: public <T> T fromJson(String json, Class<T> clazz) {
          if (json == null || json.trim().length() == 0) {
              return null;
          }
  
          try {
              return mapper.readValue(json, clazz);
          } catch (IOException e) {
              logger.warn("fromJson出错:" + json, e);
              return null;
          }
      }