JSP验证码实现

生成验证码的Servlet

import java.io.IOException;    import javax.servlet.ServletException;    import javax.servlet.http.HttpServlet;    import javax.servlet.http.HttpServletRequest;    import javax.servlet.http.HttpServletResponse;    import javax.servlet.http.HttpSession;    import java.util.*;    import java.awt.*;    import java.awt.image.*;        import javax.imageio.*;    /**  *   * @author mzba  *  */  public class GetCaptcha extends HttpServlet {        private static final long serialVersionUID = 1L;            /**       * @see HttpServlet#HttpServlet()       */        public GetCaptcha() {            super();            // TODO Auto-generated constructor stub        }            /**       * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse       *      response)       */        protected void doGet(HttpServletRequest request,                HttpServletResponse response) throws ServletException, IOException {            response.setContentType("image/jpeg");            response.setHeader("Pragma", "No-cache");            response.setHeader("Cache-Control", "no-cache");            response.setDateHeader("Expires", 0);            HttpSession session = request.getSession();            // 在内存中创建图象            int width = 75, height = 25;            BufferedImage image = new BufferedImage(width, height,                    BufferedImage.TYPE_INT_RGB);            // 获取图形上下文            Graphics g = image.getGraphics();            // 生成随机类            Random random = new Random();            // 设定背景色            g.setColor(getRandColor(200, 250));            g.fillRect(0, 0, width, height);            // 设定字体            g.setFont(new Font("Times New Roman", Font.PLAIN, 24));            // 画边框            g.setColor(getRandColor(160, 200));            g.drawRect(0, 0, width - 1, height - 1);            // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到            g.setColor(getRandColor(160, 200));            for (int i = 0; i < 155; i++) {                int x = random.nextInt(width);                int y = random.nextInt(height);                int xl = random.nextInt(12);                int yl = random.nextInt(12);                g.drawLine(x, y, x + xl, y + yl);            }            // 取随机产生的认证码(4位数字)            String sRand = "";            for (int i = 0; i < 4; i++) {                String rand = String.valueOf(random.nextInt(10));                sRand += rand;                // 将认证码显示到图象中                g.setColor(new Color(20 + random.nextInt(110), 20 + random                        .nextInt(110), 20 + random.nextInt(110)));                // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成                g.drawString(rand, 13 * i + 14, 20);            }                // 将认证码存入SESSION            session.setAttribute("vcode", sRand);                // 图象生效            g.dispose();            // 输出图象到页面            ImageIO.write(image, "JPEG", response.getOutputStream());        }            /**       * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse       *      response)       */        protected void doPost(HttpServletRequest request,                HttpServletResponse response) throws ServletException, IOException {            // TODO Auto-generated method stub        }            Color getRandColor(int fc, int bc) {// 给定范围获得随机颜色            Random random = new Random();            if (fc > 255)                fc = 255;            if (bc > 255)                bc = 255;            int r = fc + random.nextInt(bc - fc);            int g = fc + random.nextInt(bc - fc);            int b = fc + random.nextInt(bc - fc);            return new Color(r, g, b);        }        }