【总结】服务器端文件下载的方法

第一种方法：
//***********************************>> 文件下载 <<***************************************//
  ///<summary>
  /// 输出硬盘文件，提供下载 支持大文件、续传、速度限制、资源占用小
  /// </summary>
  /// <param name="_Request">Page.Request对象</param>
  /// <param name="_Response">Page.Response对象</param>
  /// <param name="_fileName">下载文件名</param>
  /// <param name="_fullPath">带文件名下载路径</param>
  /// <param name="_speed">每秒允许下载的字节数</param>
  /// 返回是否成功
  public bool ResponseFile(HttpRequest _Request,HttpResponse _Response,string _fileName,string _fullPath, long _speed)
  {   
   try
   {
    FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    BinaryReader br = new BinaryReader(myFile);
    try
    {
     _Response.AddHeader("Accept-Ranges", "bytes");
     _Response.Buffer = false;
     long fileLength = myFile.Length;
     long startBytes = 0;
    
     int pack = 10240; //10K bytes
     //int sleep = 200;   //每秒5次   即5*10K bytes每秒
     int sleep = (int)Math.Floor(1000.0 * pack / _speed) + 1;
     if (_Request.Headers["Range"] != null)
     {
      _Response.StatusCode = 206;
      string[] range = _Request.Headers["Range"].Split(new char[] {'=', '-'});
      startBytes = Convert.ToInt64(range[1]);
     }
     _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
     if (startBytes != 0)
     {
      _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength-1, fileLength));
     }
     _Response.AddHeader("Connection", "Keep-Alive");
     _Response.ContentType = "application/octet-stream";
     _Response.AddHeader("Content-Disposition","attachment;filename=" + HttpUtility.UrlEncode(_fileName,System.Text.Encoding.UTF8) );
 
     br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
     int maxCount = (int) Math.Floor(1.0*(fileLength - startBytes) / pack) + 1;

     for (int i = 0; i < maxCount; i++)
     {
      if (_Response.IsClientConnected)
      {
       _Response.BinaryWrite(br.ReadBytes(pack));
       Thread.Sleep(sleep);
      }
      else
      {
       i=maxCount;
      }
     }
     //_Response.Flush();
     //_Response.End();
    }
    catch
    {
     return false;
    }
    finally
    {
     br.Close();
     myFile.Close();
    }
   }
   catch
   {
    return false;
   }
   return true;
  }
  //****************************************************************************************//

调用实例：
Response.Clear();
bool success = ResponseFile(Request, Response, "tt.doc", @"D:\My Net\test1\tt.doc", 200 * 1024);
 if (!success)
     Alert("下载文件出错!");
 Response.End();

第二种方法：
   protected void get_download(string fl_path)
    {
        try
        {
            string filepath = fl_path;
            string filename = System.IO.Path.GetFileName(filepath);
            Response.Clear();
            Response.ClearHeaders();
            Response.Buffer = false;
            Response.ContentType = "application/octet-stream";
            //Response.ContentEncoding=System.Text.Encoding.GetEncoding("utf-8");
            Response.AddHeader("Content-Disposition", "attachment; filename=" + System.Web.HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8));
            Response.WriteFile(filepath);
            Response.Flush();
            Response.End();
        }
        catch (Exception E)
        {
            Alert("没有找到您所要下载的数据！");
        }
    }