code: public Page findPageParameter(Object paramObj) {
      Page page = null;
      if (paramObj instanceof Page) {
        page = (Page) paramObj;
      } else if (paramObj instanceof Map) {
        Map m = (Map) paramObj;
        for (Object o : m.values()) {
          if (o instanceof Page) {
            page = (Page) o;
            break;
          }
        }
      }
      if (page != null) {
        PAGE_THREAD_LOCAL.set(page);
      }
      return page;
    }
docs: 从传递的参数中找Page对象，并返回
  
  @param paramObj
  @return