/// 修改web.config文件appsettings配置节中的add里的value属性
/// </summary>
/// <remarks>
/// 注意，调用该函数后，会使整个web application重启，导致当前所有的会话丢失
/// </remarks>
/// <param name="key">要修改的键key</param>
/// <param name="strvalue">修改后的value</param>
/// <exception cref="">找不到相关的键</exception>
/// <exception cref="">权限不够，无法保存到web.config文件中</exception>
public void Modify(string key, string strvalue)
{
string xpath = "/configuration/appSettings/add[@key=?]";
XmlDocument domwebconfig = new XmlDocument();
domwebconfig.Load(HttpContext.Current.Server.MapPath("/web.config"));
XmlNode addkey = domwebconfig.SelectSingleNode((xpath.Replace("?", key)));
if (addkey == null)
{
throw new ArgumentException("没有找到<add key=" + key + " value=.../>的配置节");
}
addkey.Attributes["value"].InnerText = strvalue;
domwebconfig.Save(HttpContext.Current.Server.MapPath("/web.config"));
}