文件上传中sever.mapPath和Request.PhysicalApplicationPath用法

aspx页面代码：

 添加一个上传控件

<p>
        <asp:FileUpload ID="FileUpload1" runat="server" /><br />
        <asp:Button ID="Button2" runat="server" Text="确认上传" onclick="Button2_Click" />
</p>

 cs文件代码：

 //保存图片
  

  protected void Button2_Click(object sender, EventArgs e)
    {
        if (FileUpload1.HasFile)
        {
            //获取文件的扩展名
            string extend = System.IO.Path.GetExtension(FileUpload1.FileName).ToString();
            //设置保存路径(如在根目录下的userfiles下)
            string path = HttpContext.Current.Request.PhysicalApplicationPath + "userfiles//";
            //或者 string paths = Server.MapPath("~/") + "userfiles/";  
            //或者 string pathss = Server.MapPath("~") + @"\userfiles\";
            //自定义文件名(前缀+时间格式)   
            // string time = DateTime.Now.ToString("yyyyMMddHHmmssffff");//<年月日+时分秒+毫秒+微秒>
            string timeFormat = DateTime.Now.ToShortDateString().Replace("-", "") + DateTime.Now.Hour.ToString() + DateTime.Now.Minute.ToString() + DateTime.Now.Second.ToString() + DateTime.Now.Millisecond.ToString();
            string fileName = "xx" + timeFormat+ extend;
            FileUpload1.SaveAs(path + fileName);//或者 FileUpload1.PostedFile.SaveAs(path + fileName);     
                
        }
    }