1、导入dependency

<dependency>
    <groupId>com.github.whvcse</groupId>
    <artifactId>easy-captcha</artifactId>
    <version>1.6.2</version>
</dependency>

2、测试类

@GetMapping("/captcha")
    public ResponseResult getCaptcha(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // 设置请求头为输出图片类型
        response.setContentType("image/gif");
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);

        SpecCaptcha specCaptcha = new SpecCaptcha(130, 48, 5);
        specCaptcha.setFont(new Font("Verdana", Font.PLAIN, 32));
        // 设置类型
        specCaptcha.setCharType(Captcha.TYPE_ONLY_CHAR);

        request.getSession().setAttribute("captcha", specCaptcha.text().toLowerCase());
        specCaptcha.out(response.getOutputStream());
        return null;
    }

3、验证