生成纯数字的验证码

public class RandomCode {
    private int width = 84;
    private int height = 28;
    public void getCode(HttpServletRequest request,HttpServletResponse response) throws IOException{
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = image.createGraphics();
        
        //创建一个随机数生成器类
        Random random = new Random();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        
        //创建字体，字体的大小应该根据图片的高度来定
        Font font = new Font("雅黑", Font.ITALIC, 30);
        //设置字体
        g.setFont(font);
        //画边框
        g.setColor(Color.BLACK);
        g.drawRect(0, 0, width, height);
        //随机产生160条干扰线，使图像中的认证码不易被其他程序探测到
        g.setColor(Color.GRAY);
        for (int i = 0; i < 10; i++) {
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            int xl = random.nextInt(12);
            int yl = random.nextInt(12);
            g.drawLine(x, y, x+xl, y+yl);
        }
        //randomCode用于保存随机产生的验证码，以便用户登录后进行验证
        StringBuffer randomCode=new StringBuffer();
        int red=0,green=0,blue=0;
        //随机产生4位数字的验证码
        for (int i = 0; i < 5; i++) {
            //得到产生的随机验证码数字
            String strRand = String.valueOf(random.nextInt(10));
            //产生随机的颜色分量来构造颜色值，这样输出的每位数字的颜色值都将不同
            red=random.nextInt(200);
            green=random.nextInt(200);
            blue=random.nextInt(200);
            
            //产生随机高度13至height之间
            float imght = 0;
            while(imght<=12){
                imght = Float.parseFloat(String.valueOf(random.nextInt(height)));
            }
            //用随机产生的颜色将验证码绘制到图像中
            g.setColor(new Color(red, green, blue));
            g.drawString(strRand, 13*i+6, height);
            //将产生的四个随机数组合在一起
            randomCode.append(strRand);
        }
        //将四位数字的验证码保存到Session中
        HttpSession session = request.getSession();
        session.setAttribute("randomCode", randomCode.toString());
        //禁止图像缓存
        response.setHeader("Pragma", "no-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("image/jpeg");
        //将图像输出到Servlet输出流中
        ServletOutputStream stream = response.getOutputStream();
        ImageIO.write(image, "jpeg", stream);
        stream.close();
    }
}