/// <summary>
        /// 使用OutputStream.Write分塊下載檔案  
        /// </summary>
        /// <param name="filePath"></param>
        public void WriteFileBlock(string filePath)
        {
            filePath = Server.MapPath(filePath);
            if (!File.Exists(filePath))
            {
                
 
return;
            }
            FileInfo info = new FileInfo(filePath);
            //指定塊大小   
            long chunkSize = 4096;
            //建立一個4K的緩衝區   
            byte[] buffer = new byte[chunkSize];
            //剩餘的位元組數   
            long dataToRead = 0;
            FileStream stream = null;
            
 
try
            {
                //開啟檔案   
                stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
                
                dataToRead = stream.Length;

                //新增Http頭   
                HttpContext.Current.Response.ContentType = "application/octet-stream
 
";
                HttpContext.Current.Response.AddHeader("Content-Disposition", "attachement;filename=" + Server.UrlEncode(info.FullName));
                HttpContext.Current.Response.AddHeader("Content-Length", dataToRead.ToString());

                while (dataToRead > 0)
                {
                    if (HttpContext.Current.Response.IsClientConnected)
                    {
                        int length = stream.Read(buffer, 0, Convert.ToInt32(chunkSize));
                        HttpContext.Current.Response.OutputStream.Write(buffer, 0, length);
                        HttpContext.Current.Response.Flush();
                        HttpContext.Current.Response.Clear();
                        dataToRead -= length;
                    }
                    else
                    {
                        //防止client失去連線   
                        dataToRead = -1;
                    }
                }
            }
            catch (Exception ex)
            {
                HttpContext.Current.Response.Write("Error:" + ex.Message);
            }
            finally
            {
                if (stream != null)
                {
                    stream.Close();
                }
                HttpContext.Current.Response.Close();
            }

        }