上传图片用时间重命名防止秒的重复用到Random

知识点try：

 Random ra = new Random();//Random伪随机数生成器
            ra.Next(100, 999).ToString();
            Response.Write(ra.Next(100, 999).ToString());

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string picName = "";//生成的随机文件名
        if (File1.Value.Trim() != "")
        {
            HttpPostedFile file1 = File1.PostedFile;
            string filename = "";//不含路径的文件名
            filename = file1.FileName.Substring(file1.FileName.LastIndexOf("\\") + 1, file1.FileName.Length - file1.FileName.LastIndexOf("\\") - 1);
            string extension = System.IO.Path.GetExtension(filename).ToLower();

            if (extension == ".jpg" || extension == ".jpeg" || extension == ".gif" || extension == ".bmp")
            {
                //Response.Write("<script>alert('" + filename + "')</script>"); return;
                Random ra = new Random();
                DateTime d1 = DateTime.Now;
                picName = d1.ToString("yyyyMMddHHmmss") + ra.Next(100, 999).ToString() + extension;
                string savePath = Server.MapPath("upload/" + picName);
                file1.SaveAs(savePath);
            }
            else { Response.Write("<script>alert('不允许上传此格式文件(允许类型：jpg、jpeg、gif、bmp)！');self.location.href=self.location.href;</script>"); }
        }
//picName就是随机的重命名