Asp.net 下载功能的解决方案

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1. 首先新建一个用于进行下载处理的page页，如download.aspx，里面什么东西也没有。
2. 添加一个DownloadHandler类，它继承于IHttpHandler接口，可以用来自定义HTTP 处理程序同步处理HTTP的请求。

复制代码代码如下:

 
public class DownloadHandler : IHttpHandler 
{ 
public void ProcessRequest(HttpContext context) 
{ 
HttpResponse Response = context.Response; 
HttpRequest Request = context.Request; 
System.IO.Stream iStream = null; 
byte[] buffer = new Byte[10240]; 
int length; 
long dataToRead; 
try 
{ 
string filename = FileHelper.Decrypt(Request["fn"]); //通过解密得到文件名 
string filepath = HttpContext.Current.Server.MapPath("~/") + "files/" + filename; //待下载的文件路径 
iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open, 
System.IO.FileAccess.Read, System.IO.FileShare.Read); 
Response.Clear(); 
dataToRead = iStream.Length; 
long p = 0; 
if (Request.Headers["Range"] != null) 
{ 
Response.StatusCode = 206; 
p = long.Parse(Request.Headers["Range"].Replace("bytes=", "").Replace("-", "")); 
} 
if (p != 0) 
{ 
Response.AddHeader("Content-Range", "bytes " + p.ToString() + "-" + ((long)(dataToRead - 1)).ToString() + "/" + dataToRead.ToString()); 
} 
Response.AddHeader("Content-Length", ((long)(dataToRead - p)).ToString()); 
Response.ContentType = "application/octet-stream"; 
Response.AddHeader("Content-Disposition", "attachment; filename=" + System.Web.HttpUtility.UrlEncode(System.Text.Encoding.GetEncoding(65001).GetBytes(Path.GetFileName(filename)))); 
iStream.Position = p; 
dataToRead = dataToRead - p; 
while (dataToRead > 0) 
{ 
if (Response.IsClientConnected) 
{ 
length = iStream.Read(buffer, 0, 10240); 
Response.OutputStream.Write(buffer, 0, length); 
Response.Flush(); 
buffer = new Byte[10240]; 
dataToRead = dataToRead - length; 
} 
else 
{ 
dataToRead = -1; 
} 
} 
} 
catch (Exception ex) 
{ 
Response.Write("Error : " + ex.Message); 
} 
finally 
{ 
if (iStream != null) 
{ 
iStream.Close(); 
} 
Response.End(); 
} 
} 
public bool IsReusable 
{ 
get { return true; } 
} 
} 

3. 这里涉及到一个文件名加解密的问题，是为了防止文件具体名称暴露在状态栏中，所以添加一个FileHelper类，代码如下：

复制代码代码如下:

 
public class FileHelper 
{ 
public static string Encrypt(string filename) 
{ 
byte[] buffer = HttpContext.Current.Request.ContentEncoding.GetBytes(filename); 
return HttpUtility.UrlEncode(Convert.ToBase64String(buffer)); 
} 
public static string Decrypt(string encryptfilename) 
{ 
byte[] buffer = Convert.FromBase64String(encryptfilename); 
return HttpContext.Current.Request.ContentEncoding.GetString(buffer); 
} 
} 

利用Base64码对文件名进行加解密处理。
4. 在Web.config上，添加httpHandlers结点，如下：

复制代码代码如下:

 
<system.web> 
<httpHandlers> 
<add verb="*" path="download.aspx" type="DownloadHandler" /> 
</httpHandlers> 
</system.web> 

5. 现在新建一个aspx页面，对文件进行下载：
Default.aspx代码如下：
Default.aspx

复制代码代码如下:

 
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml" > 
<head runat="server"> 
<title>文件下载</title> 
</head> 
<body> 
<form id="form1" runat="server"> 
<div> 
<asp:HyperLink ID="link" runat="server" Text="文件下载"></asp:HyperLink> 
</div> 
</form> 
</body> 
</html> 

Default.aspx.cs代码如下：
Default.aspx.cs

复制代码代码如下:

 
using System; 
using System.Data; 
using System.Configuration; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
public partial class _Default : System.Web.UI.Page 
{ 
protected void Page_Load(object sender, EventArgs e) 
{ 
string url = FileHelper.Encrypt("DesignPattern.chm"); 
link.NavigateUrl = "~/download.aspx?fn=" + url; 
} 
} 