asp.net图片上传(带重命名)

 点击按钮上传FileUpload的图片
   protected void Button3_Click(object sender, ImageClickEventArgs e)
    {
        if (FileUpload1.HasFile)
        {
            //重命名图片
            string strFileName1 = FileUpload1.FileName;            //取到上传文件的名称
            string[] myfile = strFileName1.Split('.');               //把文件名与文件类型分开
            string dotname = myfile[myfile.Length - 1].ToString().ToLower();             //得到文件类型
            if (dotname == "gif" || dotname == "jpg")
            {
                string filepath = Path.GetFullPath(FileUpload1.PostedFile.FileName);
                Random myrdn = new Random();                    //产生随机数
                strFileName1 = DateTime.Now.ToString("yyMMddHHmm") + myrdn.Next(10000).ToString() + "." + dotname;
                string imgpath = Server.MapPath("UserImg/");
                string folder = "b