//创建一张图片        //单位:像素        BufferedImage image = new BufferedImage(200, 100, BufferedImage.TYPE_INT_RGB);                //透明的玻璃        //向画板上画内容之前必须先设置画笔.        Graphics2D gra = image.createGraphics();                gra.setColor(Color.WHITE);        //从哪个坐标开始填充, 后两个参数,矩形区域        gra.fillRect(0, 0, 200, 100);                List
     
       randList = new ArrayList
      
       ();        Random random =new Random();        for (int i = 0 ;i<4;i++) {            randList.add(random.nextInt(10));        }        //设置字体        gra.setFont(new Font("宋体",Font.ITALIC|Font.BOLD,40));        Color[] colors = new Color[]{Color.RED,Color.YELLOW,Color.BLUE,Color.GREEN,Color.PINK,Color.GRAY};        for (int i = 0; i < randList.size(); i++) {            gra.setColor(colors[random.nextInt(colors.length)]);            gra.drawString(randList.get(i)+"", i*40, 70+(random.nextInt(21)-10));        }                for (int i = 0; i < 2; i++) {            gra.setColor(colors[random.nextInt(colors.length)]);            //画横线            gra.drawLine(0, random.nextInt(101), 200, random.nextInt(101));        }                ServletOutputStream outputStream = resp.getOutputStream();        //工具类        ImageIO.write(image, "jpg", outputStream);                //把验证码放入到session中        HttpSession session = req.getSession();        session.setAttribute("code", ""+randList.get(0)+randList.get(1)+randList.get(2)+randList.get(3));