Integer width = 200; //图片大小定义
  Integer height =200;
  
        //禁止浏览器缓存
        response.addHeader("pragma", "NO-cache");
  response.addHeader("Cache-Control", "no-cache");
  response.addDateHeader("Expries", 0);

        //绘制图片
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();

        //以下填充背景颜色
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);

        //设置字体颜色
        g.setColor(Color.RED);
        Font font = new Font("Arial", Font.BOLD, 18);
        g.setFont(font);

        //绘制
        String token = "cf";
        g.drawString(token, 5, height - 2);
        g.dispose();

        //发送内容到客户端
        ServletOutputStream out = response.getOutputStream();
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        encoder.encode(image);
        out.close();
 }