循循渐进04篇 maven Response 验证码实现

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器五秒刷新一次
        resp.setHeader("refresh","3");
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片的背景颜色
        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
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //把图片写给浏览器
        ImageIO.write(image, "jpg", resp.getOutputStream());
    }
//生成随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        for(int i =0; i<7-num.length();i++){
            sb.append("0");
        }
        num = sb.toString() + num;
        return num;
    }