生成数学公式图片验证

@RequestMapping(value="/verifyCode", method=RequestMethod.GET)
    @ResponseBody
    public Result<String> getVerifyCode(HttpServletResponse response,MiaoshaUser user,
    		@RequestParam("goodsId")long goodsId) {
    	if(user == null) {
    		return Result.error(CodeMsg.SESSION_ERROR);
    	}
    	try {
    		BufferedImage image  = createVerifyCode(user, goodsId);
    		OutputStream out = response.getOutputStream();
    		ImageIO.write(image, "JPEG", out);
    		out.flush();
    		out.close();
    		return null;
    	}catch(Exception e) {
    		e.printStackTrace();
    		return Result.error(CodeMsg.MIAOSHA_FAIL);
    	}
    }

public BufferedImage createVerifyCode(MiaoshaUser 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;
	}

  生成图片公式和校验参数

public boolean checkVerifyCode(MiaoshaUser user, long goodsId, int verifyCode) {
		if(user == null || goodsId <=0) {
			return false;
		}
		Integer codeOld = redisService.get(MiaoshaKey.getMiaoshaVerifyCode, user.getId()+","+goodsId, Integer.class);
		if(codeOld == null || codeOld - verifyCode != 0 ) {
			return false;
		}
		redisService.delete(MiaoshaKey.getMiaoshaVerifyCode, user.getId()+","+goodsId);
		return true;
	}
	
	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;
		}
	}

	private static char[] ops = new char[] {'+', '-', '*'};
	/**
	 * + - * 
	 * */
	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)];
		String exp = ""+ num1 + op1 + num2 + op2 + num3;
		return exp;
	}