如何在Java中利用patchca实现一个验证码生成功能

  @RequestMapping(value = {"/captcha"})  public void captcha(HttpServletRequest request,            HttpServletResponse response, @RequestParam("w") int width, @RequestParam("h") int height, @RequestParam("n") int number) throws IOException {    ConfigurableCaptchaService cs = new ConfigurableCaptchaService();    cs.setColorFactory(new SingleColorFactory(new Color(25, 60, 170)));    cs.setFilterFactory(new CurvesRippleFilterFactory(cs.getColorFactory()));    RandomFontFactory ff = new RandomFontFactory();    ff.setMinSize(30);    ff.setMaxSize(30);    RandomWordFactory rwf = new RandomWordFactory();    rwf.setMinLength(number);    rwf.setMaxLength(number);    cs.setWordFactory(rwf);    cs.setFontFactory(ff);    cs.setHeight(height);    cs.setWidth(width);    response.setContentType("image/png");    response.setHeader("Cache-Control", "no-cache, no-store");    response.setHeader("Pragma", "no-cache");    long time = System.currentTimeMillis();    response.setDateHeader("Last-Modified", time);    response.setDateHeader("Date", time);    response.setDateHeader("Expires", time);    ServletOutputStream stream = response.getOutputStream();    String validate_code = EncoderHelper.getChallangeAndWriteImage(cs,        "png", stream);    Subject subject = SecurityUtils.getSubject();    subject.getSession().setAttribute(formAuthenticationFilter.getCaptchaParam(), validate_code);    stream.flush();    stream.close();  }