<form action="upload.ashx" method="post" enctype="multipart/form-data">
        选择文件:<input type="file" name="file1" /><br />
        <input type="submit" value="上传" />
    </form>

  public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            HttpPostedFile file1 = context.Request.Files["file1"];
            helper.uploadFile(file1, "~/upload/");//这里就是对相应方法进行调用
            context.Response.Write("ok");//提示执行成功
        }

/// <summary>
        /// 上传图片
        /// </summary>
        /// <param name="file">通过form表达提交的文件</param>
        /// <param name="virpath">文件要保存的虚拟路径</param>
        public static void uploadImg(HttpPostedFile file,string virpath)
        {          
            if (file.ContentLength > 1024 * 1024 * 4)
            {
                throw new Exception("文件不能大于4M");
            }
            string imgtype = Path.GetExtension(file.FileName);
            if(imgtype!=".jpg"&&imgtype!=".jpeg")  //图片类型进行限制
            {
                throw new Exception("请上传jpg或JPEG图片");
            }
            using (Image img = Bitmap.FromStream(file.InputStream))
            {
                string savepath = HttpContext.Current.Server.MapPath(virpath+file.FileName);
                img.Save(savepath);
            }
        }
        /// <summary>
        /// 上传文件
        /// </summary>
        /// <param name="file">通过form表达提交的文件</param>
        /// <param name="virpath">文件要保存的虚拟路径</param>
        public static void uploadFile(HttpPostedFile file, string virpath)
        {
            if (file.ContentLength > 1024 * 1024 * 6)
            {
                throw new Exception("文件不能大于6M");
            }
            string imgtype = Path.GetExtension(file.FileName);
            //imgtype对上传的文件进行限制
            if (imgtype != ".zip" && imgtype != ".mp3")
            {
                throw new Exception("只允许上传zip、rar....文件");
            }
            string dirFullPath=  HttpContext.Current.Server.MapPath(virpath);
            if (!Directory.Exists(dirFullPath))//如果文件夹不存在，则先创建文件夹
            {
                Directory.CreateDirectory(dirFullPath);
            }
            file.SaveAs(dirFullPath + file.FileName);
        }