转（Response.WriteFile 无法下载大文件解决方法）

以前用Response.WriteFile(filename)，但当遇到大文件时无法完整下载。

该方法最大的问题，它不是直接将数据抛到客户端，而是在服务器端（IIS）上缓存。当下载文件比较大时，服务器压力会很大，iis虽然支持2G大小的文件下载，但当文件上了很多M时，由于服务器以及网络等因素的影响，异常概率相当大。所以当需要下载大文件时就不能使用上面的方法了。

微软推荐以下方法代替之：

■将数据分成较小的部分，然后将其移动到输出流以供下载，从而获取这些数据。
■为用户提供用于下载文件的链接。 
■使用 Microsoft ASP 3.0 进行下载或者与 ASP 一起使用 Software Artisans FileUp。 
■创建 ISAPI 扩展以下载文件。 
■使用 FTP 下载文件。
参考文档：http://support.microsoft.com/default.aspx?scid=kb;zh-cn;812406

C#相关代码如下：

public  class FileDown
    {
         public FileDown()
        {
             //
             // TODO: 在此处添加构造函数逻辑
             //
        }
         ///   <summary>
         ///  参数为虚拟路径
         ///   </summary>
         ///   <param name="FileName"></param>
         ///   <returns></returns>
         public  static  string FileNameExtension( string FileName)
        {
             return Path.GetExtension(MapPathFile(FileName));
        }
         ///   <summary>
         ///  获取物理地址
         ///   </summary>
         ///   <param name="FileName"></param>
         ///   <returns></returns>
         public  static  string MapPathFile( string FileName)
        {
             return HttpContext.Current.Server.MapPath(FileName);
        }
         ///   <summary>
         /// 使用WriteFile下载文件，参数为文件虚拟路径
         ///   </summary>
         ///   <param name="FileName"></param>
         public  static  void DownLoadold( string FileName)
        {
             string destFileName = MapPathFile(FileName);
             //  Labelmsg.Text = destFileName;
             if (File.Exists(destFileName))
            {
                FileInfo fi =  new FileInfo(destFileName);
                HttpContext.Current.Response.Clear();
                HttpContext.Current.Response.ClearHeaders();
                HttpContext.Current.Response.Buffer =  false;
                 // HttpContext.Current.Response.AppendHeader("Content-Disposition","attachment;filename=" +HttpUtility.UrlEncode(Path.GetFileName(destFileName),System.Text.Encoding.Default));
                HttpContext.Current.Response.AppendHeader( " Content-Disposition ",  " attachment;filename= " + HttpUtility.UrlEncode(Path.GetFileName(destFileName), System.Text.Encoding.UTF8));
                HttpContext.Current.Response.AppendHeader( " Content-Length ", fi.Length.ToString());
                HttpContext.Current.Response.ContentType =  " application/octet-stream ";
                HttpContext.Current.Response.WriteFile(destFileName);
                HttpContext.Current.Response.Flush();
                HttpContext.Current.Response.End();
            }
        }
         ///   <summary>
         ///  使用OutputStream.Write分块下载文件，参数为文件虚拟路径
         ///   </summary>
         ///   <param name="FileName"></param>
         public  static  void DownLoad( string FileName)
        {
             string filePath = MapPathFile(FileName);
             // 指定块大小
             long chunkSize =  204800;
             // 建立一个200K的缓冲区
             byte[] buffer =  new  byte[chunkSize];
             // 已读的字节数
             long dataToRead =  0;
            FileStream stream =  null;
             try
            {
                 // 打开文件
                stream =  new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
                dataToRead = stream.Length;
                 // 添加Http头
                HttpContext.Current.Response.ContentType =  " application/octet-stream ";
                HttpContext.Current.Response.AddHeader( " Content-Disposition ",  " attachement;filename= " + HttpUtility.UrlEncode(Path.GetFileName(filePath)));
                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失去连接
                        dataToRead = - 1;
                    }
                }
            }
             catch (Exception ex)
            {
                HttpContext.Current.Response.Write( " Error: " + ex.Message);
            }
             finally
            {
                 if (stream !=  null)
                {
                    stream.Close();
                }
                HttpContext.Current.Response.Close();
            }
        }

         ///   <summary>
         ///  使用OutputStream.Write分块下载文件，参数为文件绝对路径
         ///   </summary>
         ///   <param name="FileName"></param>
         public  static  void DownLoadFile( string filePath)
        {
             // string filePath = MapPathFile(FileName);
             // 指定块大小
             long chunkSize =  204800;
             // 建立一个200K的缓冲区
             byte[] buffer =  new  byte[chunkSize];
             // 已读的字节数
             long dataToRead =  0;
            FileStream stream =  null;
             try
            {
                 // 打开文件
                stream =  new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
                dataToRead = stream.Length;
                 // 添加Http头
                HttpContext.Current.Response.ContentType =  " application/octet-stream ";
                HttpContext.Current.Response.AddHeader( " Content-Disposition ",  " attachement;filename= " + HttpUtility.UrlEncode(Path.GetFileName(filePath)));
                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();
                        buffer =  new Byte[chunkSize];
                        dataToRead = dataToRead - length;
                    }
                     else
                    {
                         // 防止client失去连接
                        dataToRead = - 1;
                    }
                }
            }
             catch (Exception ex)
            {
                 throw ex;
                 // HttpContext.Current.Response.Write("Error:" + ex.Message);
            }
             finally
            {
                 if (stream !=  null)
                {
                    stream.Close();
                }
                HttpContext.Current.Response.Close();
            }
        }

    } 

 

 转载于 http://www.cnblogs.com/hulang/archive/2013/02/27/2934640.html