public class AuthImg extends HttpServlet {

    /**

     *

     */

    private static final long serialVersionUID = 4975974534946437434L;

    // 设置图形验证码字符串的字体和大小

    private Font mFont = new Font("微软雅黑", Font.ITALIC, 18);

    private Random random = new Random();

    public void init() throws ServletException {

        super.init();

    }

    // 生成server响应的Service方法

    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // 阻止生成的页面被缓存，保证每次都生成新的验证码

        response.setHeader("Pragma", "No-cache");

        response.setHeader("Cache-Control", "no-cache");

        response.setDateHeader("Expires", 0);

        response.setContentType("image/jpeg");

        // 指定验证码图片的大小

        int width = 80, height = 24;

        // 生成一张新的图片

        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);

        // 在图片中绘制内容

        Graphics g = image.getGraphics();

        g.setColor(new Color(252, 252, 252));

        g.fillRect(1, 1, width, height);

        g.setColor(new Color(252, 252, 252));

        g.drawRect(0, 0, width, height);

        g.setFont(mFont);

        g.setColor(new Color(252, 252, 252));

        // 该变量用于保存系统生成的随机变量字符串

        String sRand = "";

        int colorR = random.nextInt(200);

        int colorG = random.nextInt(200);

        int colorB = random.nextInt(200);

        for (int i = 0; i < 4; i++) {

            // 取得一个随机字符串

            String tmp = getRandomChar();

            sRand += tmp;

            // 将系统生成的随机字符串加入到图片上

            g.setColor(new Color(colorR, colorG, colorB));

            g.drawString(tmp, 15 * i + 10, 20);

        }

        // 取得用户的Session

        HttpSession session = request.getSession(true);

        // 将系统生成的随机验证码加入到用户Session中

        session.setAttribute("rand", sRand);

        g.dispose();

        // 输出验证码图片

        ImageIO.write(image, "JPEG", response.getOutputStream());

    }

    // 生成随机字符串的方法

    private String getRandomChar() {

        int itmp = random.nextInt(10);

        return String.valueOf(itmp);

    }

}