使用hutool完成验证码

引入依赖

    
      cn.hutool
      hutool-all
      5.7.5
    

 protected void captcha(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        LineCaptcha lineCaptcha = new LineCaptcha(260, 100, 4, 5);
        String code = lineCaptcha.getCode();
        //将验证码存入 session
        req.getSession().setAttribute("captcha",code);

        //将验证码图片响应给前端页面
        ServletOutputStream outputStream = resp.getOutputStream();
        lineCaptcha.write(outputStream);
        outputStream.close();
    }