//建立一張圖片
        //單位:畫素
        BufferedImage image = new BufferedImage(200, 100, BufferedImage.TYPE_INT_RGB);
        
        //透明的玻璃
        //向畫板上畫內容之前必須先設定畫筆.
        Graphics2D gra = image.createGraphics();
        
        gra.setColor(Color.WHITE);
        //從哪個座標開始填充, 後兩個引數,矩形區域
        gra.fillRect(0, 0, 200, 100);
        
        List
 
<Integer> randList = new ArrayList<Integer>();
        Random random =new Random();
        for (int i = 0 ;i<4;i++) {
            randList.add(random.nextInt(10));
        }
        //設定字型
        gra.setFont(new Font("宋體",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)]);
            
 
//畫橫線
            gra.drawLine(0, random.nextInt(101), 200, random.nextInt(101));
        }
        
        ServletOutputStream outputStream = resp.getOutputStream();
        //工具類
        ImageIO.write(image, "jpg", outputStream);
        
        //把驗證碼放入到session中
        HttpSession session = req.getSession();
        session.setAttribute("code", ""+randList.get(0)+randList.get(1)+randList.get(2)+randList.get(3));