HttpHandlerFactory来根据不同的后缀名调用不通的图片生成Handler来生成图片

//有点类似简单工厂设计模式, 类似DBFactory。

using  System;
using  System.Data;
using  System.Configuration;
using  System.Web;
using  System.Web.Security;
using  System.Web.UI;
using  System.Web.UI.WebControls;
using  System.Web.UI.WebControls.WebParts;
using  System.Web.UI.HtmlControls;

public   class  ImageHandler:IHttpHandlerFactory
{
     public  ImageHandler()
    {

    }
     #region  IHttpHandlerFactory Members

    IHttpHandler IHttpHandlerFactory.GetHandler(HttpContext context,  string  requestType,  string  url,  string  pathTranslated)
    {
         string  imgType  =  context.Request.QueryString[ " ext " ];
         if  ( string .IsNullOrEmpty(imgType))
            imgType  =   " jpg " ;
        imgType  =  imgType.ToLower();

         if  (imgType  ==   " jpg " )
             return   new  JpgHandler();
         else
             return   new  GifHandler();
    }

     void  IHttpHandlerFactory.ReleaseHandler(IHttpHandler handler)
    {
         
    }

     #endregion
}

//web.config

< httpHandlers >
         < add path = " *.aspx "  verb = " * "  type = " System.Web.UI.PageHandlerFactory "  validate = " true "   />
         < add verb = " * "  path = " * "  type = " ImageHandler " />         
</ httpHandlers >