asp.net 对config文件节点值的获得与修改

 class AppSettings
    {
        public static string Config = "";
        public static string AppConfig()
        {
          
          string a =  System.IO.Path.Combine( Application.StartupPath, "App.config");//此处配置文件在程序目录下
          return a;
            //return @"D:\OAServer\OAServer\bin\Debug\App.config";
           // return Config;
        }

        public static string GetValue(string appKey)
        {
            XmlDocument xDoc = new XmlDocument();
            try
            {
                xDoc.Load(AppSettings.AppConfig());
                XmlNode xNode;
                XmlElement xElem;
                xNode = xDoc.SelectSingleNode("//appSettings");
                xElem = (XmlElement)xNode.SelectSingleNode("//add[@key='" + appKey + "']");
                if (xElem != null)
                    return xElem.GetAttribute("value");
                else
                    return "";
            }
            catch (Exception)
            {
                return "";