在servlet中生成验证码-蒲公英云

在servlet中生成验证码

红太狼 2022-05-20 07:58 245阅读 0赞

验证码

验证码的作用就是防止机器人的无限注册,导致本地数据库瞬间爆炸.今天学习servlet中生成验证码.

思路

后台servlet专门生成验证码
前台,img中src指向这个servlet的映射链接,从servlet中获取这个图片资源

代码

后台代码:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        BufferedImage bfi = new BufferedImage(80, 25, BufferedImage.TYPE_INT_RGB);
        Graphics2D graphics = (Graphics2D) bfi.getGraphics();
        // 设置背景色
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0, 0, 80, 25);
        // 设置边框
        graphics.setColor(Color.BLACK);
        graphics.drawRect(0, 0, 80-1, 25-1);
        String str = drawRandomNum(graphics);
        drawPoint(bfi);
        drawInfluencedLine(graphics);
        //禁用缓存
        response.setHeader("expries", "-1");
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setHeader("content-type","image/jpeg");
        // imageIO
        ImageIO.write(bfi, "jpg", response.getOutputStream());
    }
    // 画上点
    private void drawPoint(BufferedImage bfi) {
        int area = (int) (0.02 * 80 * 25);
        for (int i = 0; i < area; ++i) {
            int x = (int) (Math.random() * 80);
            int y = (int) (Math.random() * 25);
            bfi.setRGB(x, y, (int) (Math.random() * 255));
        }
    }
    private void drawInfluencedLine(Graphics2D g) {
        //设置验证码中的干扰线
        for (int i = 0; i < 3; i++) {
            Random random = new Random();
            //随机获取干扰线的起点和终点
            int xstart = random.nextInt(80);
            int ystart = random.nextInt(25);
            int xend = random.nextInt(80);
            int yend = random.nextInt(25);
            g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
            g.drawLine(xstart, ystart, xend, yend);
        }
    }
    // 生成随机数旋转后写入
    private String drawRandomNum(Graphics2D g) {
        char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".toCharArray();
        Random random = new Random();
        int index;
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 4; i++) {
            // 从字符数组中获得随机字符
            index = random.nextInt(chars.length);
            String value = chars[index] + "";
            // 设置随机字符的颜色
            g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
            // 字体格式
            Font font = new Font(null, Font.BOLD, 20);
            g.setFont(font);
            //生成-30~30之间的数字
            int dgree = random.nextInt(60) - 30;
            //旋转
            g.rotate(dgree * Math.PI / 180, i * 20 + 2, 23);
            // 写入字符
            g.drawString(value, i * 20 + 2, 20);
            // 把画笔再转回去,免得影响下次的弧度
            g.rotate(-dgree * Math.PI / 180, i * 20 + 2, 23);
            builder.append(value);
        }
        return builder.toString();
    }

前台代码:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <h2>这是1.html</h2>
    <img src="/jsp/ServletDemo1">
</body>
</html>