方法里包括了图片大小限制、图片尺寸、文件内容等等的判断。。。

该案例是mvc下的demo，支持单张图片上传。

public ActionResult Upload()
        {
            string imgurl = "";
            foreach (string key in Request.Files)
            {
                //这里只测试上传第一张图片file[0]
                HttpPostedFileBase file0 = Request.Files[key];

                //转换成byte,读取图片MIME类型
                Stream stream;
                int size = file0.ContentLength / 1024; //文件大小KB

                if (size > 1024)
                {
                    return Content(ReturnMsg(Enum_Return.失败, "图片不能超过1M：", null));
                }

                byte[] fileByte = new byte[2];//contentLength，这里我们只读取文件长度的前两位用于判断就好了，这样速度比较快，剩下的也用不到。
                stream = file0.InputStream;
                stream.Read(fileByte, 0, 2);//contentLength，还是取前两位

                //获取图片宽和高
                //System.Drawing.Image image = System.Drawing.Image.FromStream(stream);
                //int width = image.Width;
                //int height = image.Height;


                string fileFlag = "";
                if (fileByte != null && fileByte.Length > 0)//图片数据是否为空
                {
                    fileFlag = fileByte[0].ToString()   fileByte[1].ToString();
                }
                string[] fileTypeStr = { "255216", "7173", "6677", "13780" };//对应的图片格式jpg,gif,bmp,png
                if (fileTypeStr.Contains(fileFlag))
                {
                    string action = Request["action"];
                    string path = "/uploads/";
                    switch (action)
                    {
                        case "headimage":
                            path    = "headimage/";
                            break;
                        case "blogtype":
                            path    = "blogtype/";
                            break;
                    }
                    string fullpath = path    UserInfo.userID    "/";
                    if (!Directory.Exists(Server.MapPath(fullpath)))
                    {
                        Directory.CreateDirectory(Server.MapPath(fullpath));
                    }


                    Request.Files[key].SaveAs(Server.MapPath(fullpath   Request.Files[key].FileName));
                    imgurl = fullpath    Request.Files[key].FileName;
                }
                else
                {
                    return Content(ReturnMsg(Enum_Return.失败, "图片格式不正确："  fileFlag, null));
                }

                stream.Close();
            }

            return Content(ReturnMsg(Enum_Return.成功, "上传成功", imgurl));
        }

一般处理程序

public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "application/json";
        HttpPostedFile _upfile = context.Request.Files["File"];
        if (_upfile.ContentLength < 500000)
        {
            if (string.IsNullOrEmpty(_upfile.FileName))
            {
                 context.Response.Write("请上传图片");
            }
            string fileFullname = _upfile.FileName;
            string dataName = DateTime.Now.ToString("yyyyMMddhhmmss");
            string fileName = fileFullname.Substring(fileFullname.LastIndexOf("\\")    1);
            string type = fileFullname.Substring(fileFullname.LastIndexOf(".")    1);
            if (type == "bmp" || type == "jpg" || type == "gif" || type == "JPG" || type == "BMP" || type == "GIF")
            {
                _upfile.SaveAs(HttpContext.Current.Server.MapPath("photo")   "\\"    dataName    "."    type);
                HttpCookie cookie = new HttpCookie("photo");
                context.Response.Write("上传成功");
            }
            else
            {
                context.Response.Write("支持格式：|jpg|gif|bmp|");
            }
        }
        else
        {
            context.Response.Write("你的图片已经超过500K的大小！");
        }
    }