Response验证码实现

后端实现：需要用到java的图片类，生产一个图片 

public class ImageServlet extends HttpServlet
{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
    {
        //如何让浏览器每3秒刷新一次
        resp.setHeader("Refresh","3");
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 25, 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(0,0,80,40);
        //给图片写数据
        g.setColor(Color.BLUE);//第一次设置白色的背景，第二次写数据使用蓝色
        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
    public 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;
    }
}

  
    image
    com.yinbo.servlet.ImageServlet
  
  
    image
    /image