code: public Object getUserFromSession(HttpServletRequest request) {
      Debug.logVerbose("[JdonFramework]--> enter getUserFromSession", module);
      HttpSession session = request.getSession();
      Object model = session.getAttribute(USERMODEL);
      return model;
    }
docs: 直接从Session获取，假设Session中已经存在
  @param request HttpServletRequest
  @return Model