ASP.NET 文件下载

下载页面：
 <a href="download.ashx?url=<%=Server.UrlEncode("说明.txt")%>">下载</a>
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download.ashx
<%@ WebHandler Language="C#" Class="download" %>
using System;
using System.Web;
public class download : IHttpHandler {
   
    public void ProcessRequest (HttpContext context) {
        string url = HttpContext.Current.Server.UrlDecode(context.Request.QueryString["url"]);
        downloadfile(url);
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }
    public void downloadfile(string s_fileName)
    {
       HttpContext.Current.Response.ContentType = "application/ms-download";
       string s_path = HttpContext.Current.Server.MapPath("~/") + s_fileName;
       System.IO.FileInfo file = new System.IO.FileInfo(s_path);
       HttpContext.Current.Response.Clear();
       HttpContext.Current.Response.AddHeader("Content-Type", "application/octet-stream");
       HttpContext.Current.Response.Charset = "utf-8";
       HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + System.Web.HttpUtility.UrlEncode(file.Name, System.Text.Encoding.UTF8));
       HttpContext.Current.Response.AddHeader("Content-Length", file.Length.ToString());
       HttpContext.Current.Response.WriteFile(file.FullName);