@RequestMapping("/captcha.jpg")
public void captcha(HttpServletResponse response) throws ServletException, IOException {
response.setHeader("Cache-Control", "no-store, no-cache");
response.setContentType("image/jpeg");
// 生成文字验证码
String text = producer.createText();
// 生成图片验证码
BufferedImage image = producer.createImage(text);
// 保存到shiro session
ShiroUtils.setSessionAttribute(Constants.KAPTCHA_SESSION_KEY, text);
ServletOutputStream out = response.getOutputStream();
ImageIO.write(image, "jpg", out);
}原文：https://blog.51cto.com/11623741/2488096