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 = ;
//建立一个200K的缓冲区
byte[] buffer = new byte[chunkSize];
//已读的字节数
long dataToRead = ;
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 > )
{
if (HttpContext.Current.Response.IsClientConnected)
{
int length = stream.Read(buffer, , Convert.ToInt32(chunkSize));
HttpContext.Current.Response.OutputStream.Write(buffer, , length);
HttpContext.Current.Response.Flush();
HttpContext.Current.Response.Clear();
dataToRead -= length;
}
else
{
//防止client失去连接
dataToRead = -;
}
}
}
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 = ;
//建立一个200K的缓冲区
byte[] buffer = new byte[chunkSize];
//已读的字节数
long dataToRead = ;
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 > )
{
if (HttpContext.Current.Response.IsClientConnected)
{
int length = stream.Read(buffer, , Convert.ToInt32(chunkSize));
HttpContext.Current.Response.OutputStream.Write(buffer, , 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 = -;
}
}
}
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