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>