【.Net码农】C#实现文件下载

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();
}

}

分类:
IO

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