session cookie 验证码实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Blog.UI
{
    using System.Drawing;
    using Blog.Common;
    /// <summary>
    /// Vcode 的摘要说明
    /// </summary>
    public class Vcode : IHttpHandler,System.Web.SessionState.IRequiresSessionState
    {
        Random r = new Random();
        public void ProcessRequest(HttpContext context)
        {
            //准备一张画布
            using (Image img = new Bitmap(60, 25))
            {
                
                //准备一个画家
                Graphics g = Graphics.FromImage(img);
                //背景画白
                g.Clear(Color.White);
                //画边框
                g.DrawRectangle(Pens.Red, 0, 0, img.Width - 1, img.Height - 1);
                //画噪点线
                DrawPoints(g, img, 10);
                //得到验证码字符串
                string vcodestr = Getstring(1);
                //画字符串
                g.DrawString(vcodestr, new Font("微软雅黑", 16, FontStyle.Italic | FontStyle.Strikeout), Brushes.Blue, 0, 0);
                DrawPoints(g, img, 10);
                //将图片以jpg格式显示在outputstream流
                img.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
                //存进session
                context.Session[CommonHelper.Vcode] = vcodestr;
            }
        }
        void DrawPoints(Graphics g,Image img,int n)
        {
            for (int i = 0; i < n; i++)
            {
                int x = r.Next(0, img.Width);
                int y = r.Next(0, img.Height);
                g.DrawLine(Pens.Blue, x, y, x + r.Next(2, img.Width), y + r.Next(2, img.Width));
            }
            
        }
        string Getstring(int n)
        {
            string s = string.Empty;
            
            char[] c = new char[] { ‘1‘, ‘2‘, ‘3‘, ‘4‘, ‘5‘, ‘6‘, ‘7‘, ‘8‘, ‘9‘, ‘a‘, ‘b‘, ‘c‘,‘d‘ };
            for (int i = 0; i < n; i++)
            {
               s+=c[ r.Next(c.Length)];
            }
            return s;
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}