FileUpload过滤文件类型

protected void btnSave_Click(object sender, EventArgs e)
        {
            // 确定文件夹
            string directory = WhichDirectory();
            StringBuilder str = new StringBuilder();

            if(FileUpload1.HasFile)
            {
                // 对上传文件的类型进行过滤，该处只能传压缩文件(rar或者zip)，这种文件在火狐

                 浏览器中，叫application/octet-stream
               

                 if ((this.FileUpload1.PostedFile.ContentType == "application/x-zip-compressed")

                 || (this.FileUpload1.PostedFile.ContentType == "application/octet-stream"))
                {
                    try
                    {
                        str.AppendFormat("上传文件名: {0}", FileUpload1.FileName);

                        // 保存文件
                        string thefilepath = string.Format(HttpContext.Current.Server.MapPath(("~/

                         {0}/{1}/") FileUpload1.FileName), "资源", directory);
                        FileUpload1.SaveAs(thefilepath);

                        // 显示文件的信息
                        str.AppendFormat("<br />正在上传: {0}", FileUpload1.PostedFile.FileName);
                        str.AppendFormat("<br />文件类型: {0}",