HttpHandler生成随机码、验证码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.Web.SessionState;  //为了用到session  继承了IReadOnlySessionState才能用context.Session否则回出错
namespace Vancl.SRM.Web
{
    /// <summary>
    /// Summary description for suiji
    /// createUser:liud
    /// createDate:2012-10-12
    /// </summary>
    public class suiji : IHttpHandler, IReadOnlySessionState
    {

        public void ProcessRequest(HttpContext context)
        {
            context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
            //特别注意，如不加，单击验证图片＇看不清换一张＇，无效果．
            this.CreateCheckCodeImage(GenerateCheckCode(context, "Cookie"), context);

        }

        /// <summary>
        /// 生成随机码图片
        /// </summary>
        /// <param name="checkCode">随机码</param>
        /// <param name="context"></param>
        private void CreateCheckCodeImage(string checkCode, HttpContext context)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;
            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
            Graphics g = Graphics.FromImage(image);

            try
            {
                Random random = new Random(); // //生成随机生成器
                g.Clear(Color.White);   //清空图片背景色
                for (int i = 0; i < 25; i++)   //画图片的背景噪音线
                {
                    int x1 = random.Next(image.Width);
                    int x2 = random.Next(image.Width);
                    int y1 = random.Next(image.Height);
                    int y2 = random.Next(image.Height);

                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }
                Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(checkCode, font, brush, 2, 2);
                for (int i = 0; i < 100; i++)  //画图片的前景噪音点
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);

                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); //画图片的边框线
                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                context.Response.ClearContent();
                context.Response.ContentType = "image/Gif";
                context.Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }

        }


        /// <summary>
        /// 生成随机码
        /// </summary>
        /// <param name="context"></param>
        /// <param name="type">如果随机码保存在Cookie里，那么填写Cookie ； 如果保存在Session里，那么填写Session</param>
        /// <returns></returns>
        private string GenerateCheckCode(HttpContext context, string type)
        {
            int number;
            char code;
            string checkCode = String.Empty;
            System.Random random = new Random();
            for (int i = 0; i < 4; i++)
            {
                number = random.Next();

                if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else if (number % 3 == 0)
                    code = (char)('A' + (char)(number % 26));
                else
                    code = (char)('a' + (char)(number % 26));
                checkCode += code.ToString();
            }
            if (type == "Cookie")
            {
                HttpCookie httpCookie = new HttpCookie("CheckCode");
                //httpCookie.Domain = "";可以指定域
                httpCookie.Expires = DateTime.Now.AddDays(2);
                httpCookie.Value = checkCode;
                context.Response.Cookies.Add(httpCookie);//存到Cookie里．
            }
            else if (type == "Session")
            {
                context.Session["CheckCode"] = checkCode;  //存到Seesion里．
            }


            return checkCode;
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }

}