webform文件上传加水印

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Button1.Click += Button1_Click;
    }

    void Button1_Click(object sender, EventArgs e)
    {
        if (FileUpload1.FileName == "") 
        {
            Label1.Text = "上传的文件不能为空";
            return;
        }



        //选择上传的图片
        if (FileUpload1.PostedFile.ContentLength > (4 * 1024 * 1024))
        {
            Label1.Text = "文件过大，不能上传";
        }
        else
        {
            System.Drawing.Image img = System.Drawing.Image.FromStream(FileUpload1.FileContent);

            //绘制水印
            Graphics g = Graphics.FromImage(img);
            //添加的水印
            string s = "你好";
            //绘制的文字样式
            Font f = new Font("微团雅黑", 30);
            //绘制的颜色
            Brush b = new SolidBrush(Color.Red);
            //绘制开始的坐标
            PointF p = new PointF(50, 50);
            g.DrawString(s, f, b, p);

            //上传
            //路径
            string path = "Upload/" + DateTime.Now.ToString("yyyyMMddmmssms") + FileUpload1.FileName;
            Label1.Text = "上传成功";
            //上传的方法
            img.Save(Server.MapPath(path));
            //上传的文件在页面中显示
            Image1.ImageUrl = path;
        }

    }
}