public class DownLoad : IHttpHandler    {        public void ProcessRequest(HttpContext context)        {            context.Response.ContentType = "text/plain";            string fileName = context.Request.QueryString["filename"];            //火狐浏览器支持中文传输，编码后反倒不认了，所以要判断排除火狐浏览器再编码            string UserAgent = context.Request.ServerVariables["http_user_agent"].ToLower();            if (UserAgent.IndexOf("firefox") == -1)            {//非火狐浏览器                fileName = HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8);            }            context.Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);            context.Response.WriteFile(context.Server.MapPath("Down/") + context.Request.QueryString["filename"]); //这里一定要未编码的文件名字。否则找不到文件        }        public bool IsReusable        {            get            {                return false;            }        }    }