Java代码生成图片验证码

1、使用BufferedImage创建验证码的背景图片

2、定义一个字符串形式的数学运算字符串

3、使用ScriptEngine对字符串运算公式进行计算

4、将创建好的验证码运算答案存储到redis中，并将验证码运算公式返回前端页面

5、验证验证码是否正确的时候，将redis中的验证码答案和前端提交的答案进行对比，返回验证结果。每次验证完答案，或者更新了验证码，都需要将redis中的验证码删除或者更新。

public class VerifyCode {
	public BufferedImage createVerifyCode(User user, long goodsId) {
        if (user == null || goodsId <= 0) {
            return null;
        }
        int width = 80;
        int height = 32;
        //create the image
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        // set the background color
        g.setColor(new Color(0xDCDCDC));
        g.fillRect(0, 0, width, height);
        // draw the border
        g.setColor(Color.black);
        g.drawRect(0, 0, width - 1, height - 1);
        // create a random instance to generate the codes
        Random rdm = new Random();
        // make some confusion
        for (int i = 0; i < 50; i++) {
            int x = rdm.nextInt(width);
            int y = rdm.nextInt(height);
            g.drawOval(x, y, 0, 0);
        }
        // generate a random code
        String verifyCode = generateVerifyCode(rdm);
        g.setColor(new Color(0, 100, 0));
        g.setFont(new Font("Candara", Font.BOLD, 24));
        g.drawString(verifyCode, 8, 24);
        g.dispose();
        //把验证码存到redis中
        int rnd = calc(verifyCode);
        redisService.set(MiaoshaKey.getMiaoshaVerifyCode, user.getId()+","+goodsId, rnd);
        //输出图片
        return image;
    }
    //使用静态字符数组存储运算符号
	private static char[] ops = new char[] {'+', '-', '*'};

	//定义验证码的验证规则
	private String generateVerifyCode(Random rdm) {
        int num1 = rdm.nextInt(10);
        int num2 = rdm.nextInt(10);
        int num3 = rdm.nextInt(10);
        char op1 = ops[rdm.nextInt(3)];
        char op2 = ops[rdm.nextInt(3)];
        return ""+ num1 + op1 + num2 + op2 + num3;
    }
	//该方法使用ScriptEngine将验证码的运算规则字符串进行解析运算，并返回运算结果
	private static int calc(String exp) {
        try {
            ScriptEngineManager manager = new ScriptEngineManager();
            ScriptEngine engine = manager.getEngineByName("JavaScript");
            return (Integer)engine.eval(exp);
        }catch(Exception e) {
            e.printStackTrace();
            return 0;
        }
    }
}