/**
   * 验证码
   *
   * @param width 图片宽度
   * @param height 图片高度
   * @param number 验证码数量
   */
  @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();
  }