//文件下载功能
            FileInfo file = new System.IO.FileInfo(Server.MapPath(path));
            if (File.Exists(Server.MapPath(path)))
            {
                string name = Path.GetFileName(Server.MapPath(path));
                //存在文件
                Response.Clear();
                Response.Buffer = false;
                //通知浏览器下载文件而不是打开 
                Response.ContentType = "application/octet-stream";
                //下载的文件名
                Response.AppendHeader("content-disposition", "attachment;filename=" + name);
                //文件的大小
                Response.AppendHeader("Content-Length", file.Length.ToString());
                Response.WriteFile(path);
            }