public void pwdModify(HttpServletRequest req, HttpServletResponse resp){
        // 从session中获取用户id
        Object o = req.getSession().getAttribute(Constants.USER_SESSION);
        String oldpassword = req.getParameter("oldpassword");

        // 万能map
        HashMap<String, String> resultMap = new HashMap<String, String>();

        if (o == null) {// session失效了，session过期了
            resultMap.put("result", "sessionerror");
        }else if (StringUtils.isNullOrEmpty(oldpassword)){//输入的密码为空
            resultMap.put("result","error");
        }else {
            String userPassword = ((User) o).getUserPassword();  //Session中用户的密码
            if (userPassword.equals(oldpassword)){
                resultMap.put("result","true");
            }else{
                resultMap.put("result","false");
            }
        }

        try {
            resp.setContentType("application/json");
            PrintWriter writer = resp.getWriter();
            //JSONArray 阿里巴巴的json工具类，转换格式
            /*
            reusltMap = ["result",”sessionerror","result","errro"]
            * JSON 格式={key : Value}
            * */
           writer.write(JSONArray.toJSONString(resultMap));
           writer.flush();
           writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}