.net 升级 NetCore Config配置文件 读取

.net ConfigurationManager.AppSettings[key];读取配置文件，依赖于.net framework 库，当升级为.net core 时会读不到，此时
.net core 读取配置文件，可以直接通过读取xml节点

   public class Configs
    {
        /// <summary>
        /// 根据Key取Value值(弃用)
        /// </summary>
        /// <param name="key"></param>
        public static string GetValue(string key)
        { 
            object rel = ConfigurationManager.AppSettings[key];
            return (rel == null)?string.Empty:rel.ToString().Trim();
        }
        /// <summary>
        /// 根据Key取Value值
        /// </summary>
        /// <param name="key"></param>
        public static string GetSysConfigValue(string key)
        {
            System.Xml.XmlDocument xDoc = new System.Xml.XmlDocument();
            var configPath = System.IO.Directory.GetCurrentDirectory() + "/Configs/system.config";
            // xDoc.Load(HttpContext.Current.Server.MapPath("~/Configs/system.config"));
            xDoc.Load(configPath);
            XmlNodeList adds = xDoc.SelectNodes("//appSettings/add");
            foreach (XmlNode item in adds)
            {
                var keyStr = item.Attributes[0].Value;
                var valueStr = item.Attributes[1].Value;
                if (keyStr == key)
                {
                    return valueStr;
                }
            }
            return string.Empty;
        }
        /// <summary>
        /// 根据Key修改Value
        /// </summary>
        /// <param name="key">要修改的Key</param>
        /// <param name="value">要修改为的值</param>
        public static void SetValue(string key, string value)
        {
            System.Xml.XmlDocument xDoc = new System.Xml.XmlDocument();
            var configPath = System.IO.Directory.GetCurrentDirectory() + "/Configs/system.config";
            // xDoc.Load(HttpContext.Current.Server.MapPath("~/Configs/system.config"));
            xDoc.Load(configPath);
             
            System.Xml.XmlNode xNode;
            System.Xml.XmlElement xElem1;
            System.Xml.XmlElement xElem2;
            xNode = xDoc.SelectSingleNode("//appSettings"); 
            xElem1 = (System.Xml.XmlElement)xNode.SelectSingleNode("//add[@key='" + key + "']");
            
            if (xElem1 != null) 
            {
                xElem1.SetAttribute("value", value); 
            } 
            else
            {
                xElem2 = xDoc.CreateElement("add");
                xElem2.SetAttribute("key", key);
                xElem2.SetAttribute("value", value);
                xNode.AppendChild(xElem2);
            }
            //xDoc.Save(HttpContext.Current.Server.MapPath("~/Configs/system.config"));
            xDoc.Save(configPath);
            ConfigurationManager.RefreshSection("appSettings");
        }
        
    }