public void ProcessRequest(HttpContext context)        {            context.Response.ContentType = "text/plain";            //context.Response.Write(context.Request["cheshi1"]);            if (context.Request.Files.Count > 0)            {                for (int i = 0; i < context.Request.Files.Count; i++)                {                    HttpPostedFile file = context.Request.Files[i];                                        //检查文件类型，只接收jpg,jpeg,bmp格式                    if (file.ContentType=="image/jpeg")                    {                        //通过字符串哈希码，创建多层目录随机保存路径。                        string guid = Guid.NewGuid().ToString();                        int ram = guid.GetHashCode();                        int dirA = ram & 0xf;  //0xf ‘1111‘ 整数15                        int dirB = (ram >> 4) & 0xf;  //ram 右移4位                        int dirC = (ram >> 8) & 0xf;  //ram 右移8位                        string path = context.Server.MapPath(string.Format("Upload/{0}/{1}/{2}/", dirA.ToString(), dirB.ToString(), dirC.ToString()));                        System.IO.Directory.CreateDirectory(path); //创建目录。                        file.SaveAs(path + guid + "_" + file.FileName);                        //创建缩略图并保存                        Image image = Image.FromStream(file.InputStream);                        Image smallImg = new Bitmap(200, 200 * image.Height / image.Width);                        Graphics g = Graphics.FromImage(smallImg);                        g.DrawImage(image, 0, 0, smallImg.Width, smallImg.Height);                        smallImg.Save(path + guid + "_small" + file.FileName);                        context.Response.Write("“" + file.FileName + "”上传成功！\r\n");                    }                    else                    {                        context.Response.Write("上传文件格式错误！ is：" + file.FileName + "\r\n");                    }                }                            }            else            {                context.Response.Write("上传失败！");            }        }

    <script type="text/javascript">        window.onload = function () {            document.getElementById(‘add‘).onclick = function () {                var file1 = document.getElementById(‘file1‘);                var ext = /\.[^\.]+$/.exec(file1.value.toLowerCase());                if (ext == ‘.jpeg‘ || ext == ‘.jpg‘ || ext == ‘.bmp‘) {                    return;                }                else {                    alert(‘上传文件格式错误！‘);                    return false;                }            }        };    </script>

<form id="form1" method="post" action="AddNews.aspx" enctype="application/x-www-form-urlencoded"><input type="file" name="txtImage" id="file1" value="" /><input id="add" type="submit" value="提交" />