用System.Web.Caching.Cache保存数据类的缓存

/// The DataProvider class contains a single method, Instance(), which returns an instance of the

/// user-specified data provider class.

///

public class DataProvider

{

public static IDataProvider Instance()

{

//use the cache because the reflection used later is expensive

Cache cache = System.Web.HttpContext.Current.Cache;

if ( cache['IDataProvider'] == null )

{

//get the assembly path and class name from web.config

String prefix = '';

NameValueCollection context =

(NameValueCollection)ConfigurationSettings.GetConfig('appSettings');

if (context == null)

{

//can not get settings

return null;

}

String assemblyPath = context[prefix +

'DataProviderAssemblyPath'];

String className = context[prefix +

'DataProviderClassName'];

// assemblyPath presented in virtual form, must convert to

physical path

assemblyPath =

HttpContext.Current.Server.MapPath(HttpContext.Current.Request.ApplicationPath + '/bin/' +

assemblyPath);

// Uuse reflection to store the constructor of the class

that implements IWebForumDataProvider

try

{

cache.Insert( 'IDataProvider', Assembly.LoadFrom(

assemblyPath).GetType( className ).GetConstructor(new Type[0]), new CacheDependency(

assemblyPath ) );

}

catch (Exception)

{

// could not locate DLL file

HttpContext.Current.Response.Write('<b>ERROR:</b>

Could not locate file: <code>' + assemblyPath + '</code> or could not locate class <code>' +

className + '</code> in file.');

HttpContext.Current.Response.End();

}

}

return (IDataProvider)(

((ConstructorInfo)cache['IDataProvider']).Invoke(null) );

}

}