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(); } }