public string TeacherLogin()
        {
            object userName = System.Web.HttpContext.Current.Request["username"];
            object userPwd  = System.Web.HttpContext.Current.Request["userpwd"];
            string token    = "";
            //实例化
            DBase_UsersBll buBLL = new DBase_UsersBll();

            //判断用户是否存在
            if (buBLL.TeacherLogin(userName.ToString(), DESEncrypt.Encrypt(userPwd.ToString())).UserCode != null)
            {
                string result = string.Format("{0}|{1}|", userName, userPwd);
                token = DESEncrypt.AESEncrypt(result);
                //把令牌存入缓存
                CacheHelper.Insert(result, userName.ToString());
                return("{\"code\":\"3\",\"msg\":\"登录成功!\",\"data\":{\"username\":\"" + userName + "\",\"usercode\":\"" + userPwd + "\",\"token\":\"" + token + "\"}}");
            }
            else
            {
                //程序错误
                return("{\"code\":\"0\"," + "\"msg\":\"用户不存在!登录失败!\"}");
            }
        }