通过IHttpHandler实现图片验证码

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Text;
using System.Web;
using System.Web.SessionState;

namespace HttpModuleDemo
{
    /// <summary>
    /// VerificationCode 的摘要说明
    /// </summary>
    public class VerificationCode : IHttpHandler,IRequiresSessionState 
    {
        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "image/jpeg";
            //建立Bitmap对象，绘图
            //Bitmap:是用于处理由像素数据定义的图像的对象
            Bitmap bitmap = new Bitmap(200,60);
            //Graphics:封装一个 GDI+ 绘图图面
            Graphics graph = Graphics.FromImage(bitmap);
            graph.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
            Random r = new Random();
            string letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ";
            string letter;
            StringBuilder s = new StringBuilder();
            
            //添加随机的五个字母
            for (int x = 0; x < 5; x++)
            {
                letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
                s.Append(letter);
                graph.DrawString(letter, font, new SolidBrush(Color.Black), x * 38, r.Next(0, 15));
            }
            /*
            //混淆背景
            Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
            for (int x = 0; x < 6; x++)
                graph.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            */
            //将图片保存到输出流中      
            bitmap.Save(context.Response.OutputStream, ImageFormat.Jpeg);

            ////如果没有实现IRequiresSessionState，则这里会出错，也无法生成图片
            context.Session["CheckCode"] = s.ToString();
            context.Response.End();   
        }

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