Java web 驗證碼的生成

public class CheckCodeServlet extends HttpServlet {

        public void servlet(HttpServletRequest request, HttpServletResponse response)
                        throws ServletException, IOException {
                // 畫畫
                BufferedImage image = new BufferedImage(60, 20,
                                BufferedImage.TYPE_INT_RGB);
                Graphics g = image.getGraphics();
                Random r = new Random();
                g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
                g.fillRect(0, 0, 60, 20);
                // 生成一個隨機數，而且畫到內存映射對象上
                String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
                String number = "";
                for (int i = 0; i < 5; i++) {
                        number += str.charAt(r.nextInt(str.length()));
                }

                HttpSession session = request.getSession();
                session.setAttribute("number", number);
                System.out.println(number);
                g.setColor(new Color(0, 0, 0));
                g.drawString(number, 10, 15);
                // 加一些干擾線
                for (int i = 0; i < 5; i++) {
                        g
                                        .setColor(new Color(r.nextInt(255), r.nextInt(255), r
                                                        .nextInt(255)));
                        g.drawLine(r.nextInt(60), r.nextInt(20), r.nextInt(60), r
                                        .nextInt(20));
                }
                // 2 將圖片壓縮並輸出到客戶端
                response.setContentType("image/jpeg");
                OutputStream ops = response.getOutputStream();
                javax.imageio.ImageIO.write(image, "jpeg", ops);
        }

}