(一).功能

用HttpHandler实现图片验证码

(二).代码如下

1. 处理程序文件 ValidateImage.ashx代码如下

    /// <summary>
    /// ValidateImage 生成网站验证码功能
    /// </summary>
    public class ValidateImage : IHttpHandler, IRequiresSessionState
    {
        int intLength = 5; //长度
        string strIdentify = "Identify"; //随机字串存储键值，以便存储到Session中
        public ValidateImage()
        {
        }

        /// <summary>
        /// 生成验证图片核心代码
        /// </summary>
        /// <param name="hc"></param>
        public void ProcessRequest(HttpContext hc)
        {
            //设置输出流图片格式
            hc.Response.ContentType = "image/gif";

            Bitmap b = new Bitmap(200, 60);
            Graphics g = Graphics.FromImage(b);
            g.FillRectangle(new SolidBrush(Color.YellowGreen), 0, 0, 200, 60);
            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
            Random r = new Random();

            //合法随机显示字符列表
            string strLetters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
            StringBuilder s = new StringBuilder();

            //将随机生成的字符串绘制到图片上
            for (int i = 0; i < intLength; i++)
            {
                s.Append(strLetters.Substring(r.Next(0, strLetters.Length - 1), 1));
                g.DrawString(s[s.Length - 1].ToString(), font, new SolidBrush(Color.Blue), i * 38, r.Next(0, 15));
            }

            //生成干扰线条
            Pen pen = new Pen(new SolidBrush(Color.Blue), 2);
            for (int i = 0; i < 10; i++)
            {
                g.DrawLine(pen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            }
            b.Save(hc.Response.OutputStream, ImageFormat.Gif);
            hc.Session[strIdentify] = s.ToString(); //先保存在Session中，验证与用户输入是否一致
            hc.Response.End();

        }

        /// <summary>
        /// 表示此类实例是否可以被多个请求共用(重用可以提高性能)
        /// </summary>
        public bool IsReusable
        {
            get
            {
                return true;
            }
        }
    }