.net下载

1，Http 协议中有专门的指令来告知浏览器, 本次响应的是一个需要下载的文件. 格式如下: Content-Disposition: attachment;filename=filename.ext 以上指令即标记此次响应流是附件,且附件文件名为 filename.ext 注意： (1): 中文文件名需要进行URLEncode编码, 否则在IE 6 下会提示是”无法识别的文件”.
但经实际测试,在Chrome下不进行URLEncode编码, 也能正常显示.
(2): 文件名不能有空格, 否则也会被认为是”无法识别的文件”.
(3): [ASP.Net中] 向响应流中添加该指令必须使用 response.AddHeader() 函数; 使用
response.Header.Add() 则会报错.
下面是一个实现下载文件功能的函数：

       /// <summary>
        /// 使用微软的TransmitFile下载文件
        /// </summary>
        /// <param name="filePath">服务器相对路径</param>
        public void TransmitFile(string filePath)
        {
            try
            {
                filePath = Server.MapPath(filePath);
                if (File.Exists(filePath))
                {
                    FileInfo info = new FileInfo(filePath);
                    long fileSize = info.Length;
                    HttpContext.Current.Response.Clear();                    

                    //指定Http Mime格式为压缩包
                    HttpContext.Current.Response.ContentType = "application/x-zip-compressed";

                     // Http 协议中有专门的指令来告知浏览器, 本次响应的是一个需要下载的文件. 格式如下:
                    // Content-Disposition: attachment;filename=filename.txt
                    HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + Server.UrlEncode(info.FullName));
                    //不指明Content-Length用Flush的话不会显示下载进度
                    HttpContext.Current.Response.AddHeader("Content-Length", fileSize.ToString());
                    HttpContext.Current.Response.TransmitFile(filePath, 0, fileSize);
                    HttpContext.Current.Response.Flush();
                }
            }
            catch
            { }
            finally
            {
                HttpContext.Current.Response.Close();
            }

        }

2 下面是使用WriteFile实现下载

        /// <summary>
        /// 使用WriteFile下载文件
        /// </summary>
        /// <param name="filePath">相对路径</param>
        public void WriteFile(string filePath)
        {
            try
            {
                filePath = Server.MapPath(filePath);
                if (File.Exists(filePath))
                {
                    FileInfo info = new FileInfo(filePath);
                    long fileSize = info.Length;
                    HttpContext.Current.Response.Clear();
                    HttpContext.Current.Response.ContentType = "application/octet-stream";
                    HttpContext.Current.Response.AddHeader("Content-Disposition", "attachement;filename=" + Server.UrlEncode(info.FullName));
                    //指定文件大小
                    HttpContext.Current.Response.AddHeader("Content-Length", fileSize.ToString());
                    HttpContext.Current.Response.WriteFile(filePath, 0, fileSize);
                    HttpContext.Current.Response.Flush();
                }
            }
            catch
            { }
            finally
            {
                HttpContext.Current.Response.Close();
            }
        }

3，下面是分块实现下载：

        /// <summary>
        /// 使用OutputStream.Write分块下载文件
        /// </summary>
        /// <param name="filePath"></param>
        public void WriteFileBlock(string filePath)
        {
            filePath = Server.MapPath(filePath);
            if (!File.Exists(filePath))
            {
                return;
            }
            FileInfo info = new FileInfo(filePath);
            //指定块大小
            long chunkSize = 4096;
            //建立一个4K的缓冲区
            byte[] buffer = new byte[chunkSize];
            //剩余的字节数
            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=" + 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失去连接
                        dataToRead = -1;
                    }
                }
            }
            catch (Exception ex)
            {
                HttpContext.Current.Response.Write("Error:" + ex.Message);
            }
            finally
            {
                if (stream != null)
                {
                    stream.Close();
                }
                HttpContext.Current.Response.Close();
            }

        }

public void DownLoadFile(string filePath, bool isUrl)     {         string fileName = "aaa.txt";//客户端保存的文件名

if (isUrl)         {             try             {                 filePath = Server.MapPath(filePath);             }             catch { }         }

System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);         fileName = fileInfo.Name;         if (fileInfo.Exists == true)         {             string strContentType = "";             string fileExtension = fileInfo.Extension.ToLower();             switch (fileExtension)             {                 case ".mp3":                     strContentType = "audio/mpeg3";                     break;                 case ".mpeg":                     strContentType = "video/mpeg";                     break;                 case ".jpg":                     strContentType = "image/jpeg";                     break;                 case ".bmp":                     strContentType = "image/bmp";                     break;                 case ".gif":                     strContentType = "image/gif";                     break;                 case ".doc":                     strContentType = "application/msword";                     break;                 case ".docx":                     strContentType = "application/msword";                     break;                 case ".ppt":                     strContentType = "application/vnd.ms-powerpoint";                     break;                 case ".pptx":                     strContentType = "application/vnd.ms-powerpoint";                     break;                 case ".xls":                     strContentType = "application/vnd.ms-excel";                     break;                 case ".xlsx":                     strContentType = "application/vnd.ms-excel";                     break;                 case ".pdf":                     strContentType = "application/pdf";                     break;                 case ".css":                     strContentType = "text/css";                     break;                 case ".html":                     strContentType = "text/html";                     break;                 case ".htm":                     strContentType = "text/html";                     break;                 case ".swf":                     strContentType = "application/x-shockwave-flash";                     break;                 case ".exe":                     strContentType = "application/octet-stream";                     break;                 case ".inf":                     strContentType = "application/x-texinfo";                     break;                 default:                     strContentType = "application/octet-stream";                     break;             }

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();             Response.ClearHeaders();             System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);             long dataLengthToRead = iStream.Length;//获取下载的文件总大小             Response.Charset = "utf-8";             Response.ContentEncoding = System.Text.Encoding.UTF8;

Response.ContentType = strContentType;             Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, Encoding.UTF8));             while (dataLengthToRead > 0 && Response.IsClientConnected)             {                 int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小                 Response.OutputStream.Write(buffer, 0, lengthRead);                 Response.Flush();                 dataLengthToRead = dataLengthToRead - lengthRead;             }             Response.End();         }     }