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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) );
}
}
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