图片上传并进行格式的判断

Question

if (UpLoad())
            {
                //得到上传文件的全路径
                string fullName = this.FileUpload1.PostedFile.FileName;
                //HiddenField1.Value = this.FileUpload1.PostedFile.FileName;
                //截取文件路径"\"后的字符(包括"\",所有索引值要加1)
                string fileName = fullName.Substring(fullName.LastIndexOf("\\") + 1);
                //截取文件路径"."后的字符(包括".",所有索引值要加1)
                string type = fullName.Substring(fullName.LastIndexOf(".") + 1).ToLower();
                minf.PhotoLJ = HiddenField1.Value;
            }
            return minf;--返回一个实体对象
        }        private bool UpLoad()
        {
            //string folderNews = string.Format("F:/Web/zxyAdmin/Exhibit/chenou");
            string folderNews = Server.MapPath("Photo\\"); 
            if (!System.IO.Directory.Exists(folderNews))
            {
                System.IO.Directory.CreateDirectory(folderNews);
            }//得到上传文件的全路径
                string fullName = this.FileUpload1.PostedFile.FileName;
                if (string.IsNullOrEmpty(fullName)) return true;
                //截取文件路径"\"后的字符(包括"\",所有索引值要加1)
                string fileName = fullName.Substring(fullName.LastIndexOf("\\") + 1);
                //截取文件路径"."后的字符(包括".",所有索引值要加1)
                string type = fullName.Substring(fullName.LastIndexOf(".") + 1).ToLower();
                //if (type == "bmp" || type == "jpg" || type == "gif")
                if (type == "jpg" || type == "bmp" || type == "gif")
                {
                    if (FileUpload1.PostedFile.ContentLength > 1024 * 1024)
                    {
                        Page.ClientScript.RegisterStartupScript(GetType(), "big", "<script language='javascript'>alert('你上传的图片不能超过1M!')</script>");
                        return false;
                    }
                    this.FileUpload1.SaveAs(Server.MapPath("Photo\\") + UpLoadPhotoName + "." + type);
                    HiddenField1.Value = "/zxyAdmin/Exhibit/Photo/" + UpLoadPhotoName + "." + type;
                    return true;
                }
                else
                {                    //不是合法格式做的处理
                    Page.ClientScript.RegisterStartupScript(GetType(), "scsp", "<script language='javascript'>alert('你图片上传的格式不正确!')</script>");
                    return false;
                }
            //}        }