/// <summary>
        /// 修改web.config文件appsettings配置節(jié)中的add里的value屬性
        /// </summary>
        /// <remarks>
        /// 注意，調(diào)用該函數(shù)后，會使整個web application重啟，導(dǎo)致當(dāng)前所有的會話丟失
        /// </remarks>
        /// <param >要修改的鍵key</param>
        /// <param >修改后的value</param>
        /// <exception cref="">找不到相關(guān)的鍵</exception>
        /// <exception cref="">權(quán)限不夠，無法保存到web.config文件中</exception>
        public void ModifyConfig(string path,string key, string strvalue)
        {
            string xpath = "/configuration/ZFrameConfiguration/add[@key=?]";
            XmlDocument domwebconfig = new XmlDocument();
            //domwebconfig.Load(HttpContext.Current.Server.MapPath("/web.config"));
            domwebconfig.Load(path+"http://file//web.config/");
            XmlNode addkey = domwebconfig.SelectSingleNode((xpath.Replace("?", key)));
            if (addkey == null)
            {
                throw new ArgumentException("沒有找到<add key=" + key + " value=.../>的配置節(jié)");
            }
            addkey.Attributes["value"].InnerText = strvalue;
            //domwebconfig.Save(HttpContext.Current.Server.MapPath("/web.config"));
            domwebconfig.Save(path+"http://file//web.config/");

        }