java 生成图形验证码

 public void getCode(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // 让浏览器60秒自动刷新一下次（可以不写）
        response.setHeader("refresh","60");
        // 在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_3BYTE_BGR);
        // 得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();
        // 设置图片背景色
        g.setColor(Color.white);
        g.fillRect(0,0,80,20);
        // 给图片写数据
        g.setColor(Color.blue);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0 ,20);
        // 告诉浏览器，这个请求用图片的方式打开
        response.setContentType("image/jpg");
        // 网站存在缓存，不让浏览器缓存(如下代码可以不写)
        response.setDateHeader("expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no=cache");

        // 把图片写给浏览器
        ImageIO.write(image,"jpg", response.getOutputStream());
    }

    
    private String makeNum () {
        Random random = new Random();
        String num = random.nextInt(999999) + "";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i=0; i< 6-num.length(); i++){
            stringBuffer.append("0");
        }
        num = stringBuffer.toString() + num;
        return num;
    }