/// <summary>           /// 写入web.config           /// </summary>           /// <param name="item">appSettings等</param>           /// <param name="key">键</param>           /// <param name="value">值</param>           public void WriteConfig(string item, string key, string value)           {               if (item == "")              {                  item = "appSettings";              }              Configuration config = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration(System.Web.HttpContext.Current.Request.ApplicationPath);              AppSettingsSection appSection = (AppSettingsSection)config.GetSection(item);              if (appSection.Settings[key] == null)              {                  appSection.Settings.Add(key, value);                  config.Save();              }              else              {                  appSection.Settings.Remove(key);                  appSection.Settings.Add(key, value);                  config.Save();             }          }