随机生成验证码

Posted 2020-12-18 lsxsx

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //使浏览器3秒自动刷新一次
    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 graphics = (Graphics2D) image.getGraphics();//得到画笔
    //设置图片的背景颜色
    graphics.setColor(Color.blue);
    graphics.fillRect(0, 0, 80, 20);
    //给图片写数据
    graphics.setColor(Color.white);
    graphics.setFont(new Font(null,Font.BOLD,20));
    graphics.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());

}

private String makeNum() {
    Random random = new Random();
    String num = random.nextInt(99999) + "";
    StringBuffer sb = new StringBuffer();
    for (int i = 0; i < 7 - num.length(); i++) {
        sb.append("0");
    }
    num = sb.toString() + num;
    return num;
}