生成验证码

代码实现：

public class Main {

    /**
     * 验证码字符个数
     */
    private static final int CHAR_NUM = 4;
    /**
     * 遮挡线条数
     */
    private static final int LINE_NUM = 15;

    public static void main(String[] args) {
        createImage();
    }

    private static void createImage() {
        try {
            // 定义图片宽高
            int width = 100;
            int height = 50;
            // 在内存中创建图片
            BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            // 绘制背景和边框
            Graphics g = image.getGraphics();
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, width, height);
            g.setColor(Color.BLACK);
            g.drawRect(0, 0, width - 1, height - 1);
            // 创建随机字符集和随机数对象
            String str = "ABCDEFGHIJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz23456789";
            Random random = new Random();
            for (int i = 0; i < CHAR_NUM; i++) {
                // 获取随机字符
                int index = random.nextInt(str.length());
                char ch = str.charAt(index);
                // 获取随机颜色
                Color randomColor = getRandomColor(random);
                g.setColor(randomColor);
                // 设置字体
                Font font = new Font("微软雅黑", Font.BOLD, height / 2);
                g.setFont(font);
                // 写入验证码
                g.drawString(ch + "", (i == 0) ? width / 4 * i + 2 : width / 4 * i, height - height / 4);
            }
            // 绘制干扰线
            for (int i = 0; i < LINE_NUM; i++) {
                int x1 = random.nextInt(width);
                int x2 = random.nextInt(width);
                int y1 = random.nextInt(height);
                int y2 = random.nextInt(height);
                Color randomColor = getRandomColor(random);
                g.setColor(randomColor);
                g.drawLine(x1, y1, x2, y2);
            }
            File file = new File("image.jpg");
            FileOutputStream out = new FileOutputStream(file);
            // 写入文件
            ImageIO.write(image, "jpg", out);
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 随机颜色生成方法
     *
     * @param random 随机对象
     * @return 随机颜色
     */
    private static Color getRandomColor(Random random) {
        int colorIndex = random.nextInt(3);
        switch (colorIndex) {
            case 1:
                return Color.BLUE;
            case 2:
                return Color.GREEN;
            case 3:
                return Color.RED;
            default:
                return Color.MAGENTA;
        }
    }

}

生成结果：

image.jpg