Code

public class Download : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        //得到请求的路径  
        string path = context.Server.UrlDecode(context.Request.QueryString["file"]);
        System.IO.FileStream fs = System.IO.File.Open(path, System.IO.FileMode.Open);
        context.Response.Clear();
        string p = path.Substring(path.LastIndexOf("/") + 1);
        string strTemp = System.Web.HttpUtility.UrlEncode(p, System.Text.Encoding.UTF8);//解决文件名乱码
        context.Response.AddHeader("content-disposition", "attachment;filename=" + strTemp);
        context.Response.ContentType = "application/octet-stream";
        int b = fs.ReadByte();
        while (b != -1)
        {
            context.Response.BinaryWrite(new byte[] { (byte)b });
            b = fs.ReadByte();
        }
        fs.Close();
        
        HttpContext.Current.ApplicationInstance.CompleteRequest();
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}