Java怎么实现图形验证码 Java生成图片验证码完整示例

@WebServlet("/code")
public class CaptchaServlet extends HttpServlet {
    private static final int WIDTH = 80;
    private static final int HEIGHT = 30;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        // 1. 创建图片缓冲区
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = image.createGraphics();

        // 2. 设置背景颜色
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, WIDTH, HEIGHT);

        // 3. 添加干扰线
        g.setColor(Color.GRAY);
        for (int i = 0; i < 5; i++) {
            int x1 = (int)(Math.random() * WIDTH);
            int y1 = (int)(Math.random() * HEIGHT);
            int x2 = (int)(Math.random() * WIDTH);
            int y2 = (int)(Math.random() * HEIGHT);
            g.drawLine(x1, y1, x2, y2);
        }

        // 4. 生成随机验证码文本
        String base = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        StringBuilder sb = new StringBuilder();
        Random random = new Random();
        for (int i = 0; i < 4; i++) {
            char c = base.charAt(random.nextInt(base.length()));
            sb.append(c);
        }
        String code = sb.toString();

        // 存储到session中用于后续验证
        req.getSession().setAttribute("captcha", code);

        // 5. 绘制文字
        g.setFont(new Font("Arial", Font.BOLD, 20));
        g.setColor(Color.BLUE);
        for (int i = 0; i < code.length(); i++) {
            char c = code.charAt(i);
            g.drawString(String.valueOf(c), 15 + i * 15, 20);
        }

        // 6. 释放资源
        g.dispose();

        // 7. 输出图片
        resp.setContentType("image/jpeg");
        ImageIO.write(image, "JPEG", resp.getOutputStream());
    }
}

<img src="/code" onclick="this.src='/code?'+Math.random()" alt="验证码" style="cursor:pointer;">