以流的方式下载文件

   public static void DownLoad(string FullFileName)
        {
            var DownloadFile = new FileInfo(HostingEnvironment.ApplicationPhysicalPath + FullFileName);
            HttpContext.Current.Response.Clear();

            HttpContext.Current.Response.ClearHeaders();

            HttpContext.Current.Response.Buffer = false;

            HttpContext.Current.Response.ContentType = "application/octet-stream";

            HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(FullFileName, System.Text.Encoding.UTF8));

            HttpContext.Current.Response.AppendHeader("Content-Length", DownloadFile.Length.ToString());

            HttpContext.Current.Response.WriteFile(DownloadFile.FullName);

            HttpContext.Current.Response.Flush();

            HttpContext.Current.Response.End();

        }