ASP.net流的方式输出图片或文件

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.IO;
public partial class admin_showimg : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string img = Request.QueryString["img"];
        string pic;
        if (img == null || img == "")
        {
            pic = Server.MapPath("/images/nopic.jpg");
        }
        else
        {
            pic = Server.MapPath("/") + img;
        }
        if (File.Exists(pic))
        {
            Response.ContentType = "image/jpg";
            Response.WriteFile(pic);
        }
    }
}