依赖

<dependency>
      <groupId>com.github.penggle</groupId>
      <artifactId>kaptcha</artifactId>
      <version>2.3.2</version>
  </dependency>

配置KaptchaConfig

@Configuration
public class KaptchaConfig {
    @Bean
    public Producer kaptchaProducer() {
        Properties properties = new Properties();
        properties.setProperty("kaptcha.image.width", "100");
        properties.setProperty("kaptcha.image.height", "40");
        properties.setProperty("kaptcha.textproducer.font.size", "32");
        properties.setProperty("kaptcha.textproducer.font.color", "0,0,0");
        properties.setProperty("kaptcha.textproducer.char.string", "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYAZ");
        properties.setProperty("kaptcha.textproducer.char.length", "4");
        properties.setProperty("kaptcha.noise.impl", "com.google.code.kaptcha.impl.NoNoise");

        DefaultKaptcha kaptcha = new DefaultKaptcha();
        Config config = new Config(properties);
        kaptcha.setConfig(config);
        return kaptcha;
    }
}

获取验证码

private static final Logger logger = LoggerFactory.getLogger(LoginController.class);
@Autowired
private Producer producer;

@GetMapping("/kaptcha")
public void getKaptcha(HttpServletResponse response, HttpSession session) {
    String text = producer.createText();
    BufferedImage image = producer.createImage(text);

    // 存储到session
    session.setAttribute("kaptcha", text);
    response.setContentType("image/png");
    try {
        ServletOutputStream outputStream = response.getOutputStream();
        ImageIO.write(image, "png", outputStream);
    } catch (IOException e) {
        logger.error("创建验证码失败" + e.getMessage());
    }
}