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利用IhttpHandler实现文件下载

WebUIASPXHTMLSecurity 
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1. 首先新建一个用于下载文件的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。

using System.Web;
using System;
using System.IO;
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：

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：

<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：

<%@ 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：

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;
    }
}
 这样就实现了文件下载时,不管是什么格式的文件,都能够弹出打开/保存窗口。
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