/// <summary>

     /// 提供对配置信息的访问

     /// </summary>

     public static class AppSettings

     {

         /// <summary>

         /// 配置信息

         /// </summary>

         private static volatile NameValueCollection _appSettingsCollection;

         /// <summary>

         /// 配置信息属性

         /// </summary>

         private static NameValueCollection AppSettingsCollection

         {

             get

             {

                 return _appSettingsCollection ?? ReloadAppSettings();

             }

         }

         /// <summary>

         /// 重新加载配置信息

         /// </summary>

         /// <returns></returns>

         static NameValueCollection ReloadAppSettings()

         {

             var nameValueCollection = new NameValueCollection();

             //从数据库读取配置

                 xxx.ToList()

                 .ForEach(entity =>

                 {

                     nameValueCollection[entity.Name] = entity.Value;

                 });

             LastAppSettingsDateTime = DateTime.Now;

             _appSettingsCollection = nameValueCollection;

             return _appSettingsCollection;

         }

         /// <summary>

         /// 在启动时以后台任务刷新配置信息

         /// </summary>

         static AppSettings()

         {

             Task.Factory.StartNew(() =>

             {

                 //按配置间隔分钟刷新配置信息

                 for (; ; )

                 {

                     try

                     {

                         //取配置的间隔分钟，默认为1分钟

                         double minutes;

                         if (_appSettingsCollection == null

                             || !double.TryParse(_appSettingsCollection["AppSettingsRefreshIntervalMinutes"], out minutes)

                             || minutes < 0.1)

                             minutes = 1D;

                         Task.Delay(TimeSpan.FromMinutes(minutes)).Wait();

                         ReloadAppSettings();

                     }

                     catch (Exception ex)

                     {

                     }

                 }

             }, TaskCreationOptions.LongRunning);

         }

         /// <summary>

         /// 获取配置信息

         /// </summary>

         /// <param name="name"></param>

         /// <returns></returns>

         public static string Get(string name)

         {

             return AppSettingsCollection[name];

         }

         /// <summary>

         /// 最后获取配置信息的时间

         /// </summary>

         public static DateTime LastAppSettingsDateTime { get; private set; }

     }