.NET使用一般處理常式產生驗證碼

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using System;    using System.Web;    using System.Drawing;    using System.Drawing.Drawing2D;    using System.Web.SessionState;         public class WaterMark : IHttpHandler, IRequiresSessionState  //  要使用session必須實現該介面,記得要匯入System.Web.SessionState命名空間    {           public void ProcessRequest(HttpContext context)        {            string checkCode = GenCode(5);  // 產生5位隨機字元            context.Session["Code"] = checkCode; //將字串儲存到Session中，以便需要時進行驗證            System.Drawing.Bitmap image = new System.Drawing.Bitmap(70, 22);            Graphics g = Graphics.FromImage(image);            try           {                //產生隨機產生器                Random random = new Random();                   //清空圖片背景色                g.Clear(Color.White);                   // 畫圖片的背景雜音線                int i;                for (i = 0; i < 25; i++)                {                    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.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);                   //畫圖片的前景噪音點                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);                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>    /// 產生隨機字串    /// </summary>    /// <param name="num">隨機出幾個字元</param>    /// <returns>隨機出的字串</returns>     private string GenCode(int num)        {            string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";         char[] chastr = str.ToCharArray();            // string[] source ={ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "#", "$", "%", "&", "@" };            string code = "";            Random rd = new Random();            int i;            for (i = 0; i < num; i++)            {                //code += source[rd.Next(0, source.Length)];                code += str.Substring(rd.Next(0, str.Length), 1);            }            return code;           }           public bool IsReusable        {            get           {                return false;            }        }       }