分块下载

 public void FileDownload4()
        {
            string fileName = "大数据.rar";//客户端保存的文件名 
            string filePath = Server.MapPath("/App_Data/大数据.rar");//要被下载的文件路径  

            if (System.IO.File.Exists(filePath))
            {
                const long ChunkSize = 102400; //100K 每次读取文件，只读取100K，这样可以缓解服务器的压力 
                byte[] buffer = new byte[ChunkSize];

                Response.Clear();
                using (FileStream fileStream = System.IO.File.OpenRead(filePath))
                {
                    long fileSize = fileStream.Length; //文件大小 
                    Response.ContentType = "application/octet-stream"; //二进制流
                    Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));//下载保存的文件名
                    Response.AddHeader("Content-Length", fileStream.Length.ToString());//文件总大小
                    while (fileSize > 0 && Response.IsClientConnected)//判断客户端是否还连接了服务器
                    {
                        //实际读取的大小 
                        int readSize = fileStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));
                        Response.OutputStream.Write(buffer, 0, readSize);
                        Response.Flush();//如果客户端 暂停下载时，这里会阻塞。
                        fileSize = fileSize - readSize;//文件剩余大小
                    }
                }
                Response.Close();
            }
        }