public class FrequencyInterceptor implements HandlerInterceptor {

    /**
     * 最大限制
     */
    private final int maxLimit;

    /**
     * 时间段
     */
    private final int periodInSeconds;


    RedisTemplate<String, Object> redisTemplate;

    public FrequencyInterceptor(int maxLimit, int periodInSeconds, RedisTemplate<String, Object> redisTemplate) {
        this.maxLimit = maxLimit;
        this.periodInSeconds = periodInSeconds;
        this.redisTemplate = redisTemplate;
    }


    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String ipAddr = IpUtil.getIpAddr(request);
        String userAgent = request.getHeader("user-agent");

        MessageDigest md5 = MessageDigest.getInstance("md5");
        byte[] digest = md5.digest((ipAddr + userAgent).getBytes(StandardCharsets.UTF_8));
        final String ipAndUa = new BigInteger(1, md5.digest()).toString(16);


        String key = "send_msg_limit:" + ipAndUa;
        Integer limit = (Integer) redisTemplate.opsForValue().get(key);
        if (limit == null) {
            // 此处可能高并发
            Long newValue = redisTemplate.opsForValue().increment(key);
            if (newValue == null) {
                // 出错
                throw new RuntimeException("网络繁忙，请稍后重试");
            }
            // 只需考虑第一个设置过期时间
            if (newValue == 1) {
                redisTemplate.expire(key, Duration.ofSeconds(periodInSeconds));
                return true;
            } else if (newValue <= maxLimit) {
                return true;
            } else {
                // 如果是溢出请求，全部打回
                throw new RuntimeException("操作频繁，请稍后重试");
            }
        } else if (limit > 5) {
            // 一般情况，溢出打回
            throw new RuntimeException("操作频繁，请稍后重试");
        } else {
            Long newValue = redisTemplate.opsForValue().increment(key);
            if (newValue == null) {
                throw new RuntimeException("网络繁忙，请稍后重试");
            }
            if (newValue <= maxLimit) {
                return true;
            } else {
                throw new RuntimeException("操作频繁，请稍后重试");
            }
        }
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle...");
    }


    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion...");
    }
}