你好：
我有一个疑问，当Registry调用destroy后不会去清除AbstractRegistryFactory中的缓存，导致以同样的参数再次获取的时候得到了一个已经无法使用的Registry。这个时设计的时候就认为不该这么使用吗？
}
    @Override
    public void unregister(URL url) {
        if (url == null) {
            throw new IllegalArgumentException("unregister url == null");
        }
        if (logger.isInfoEnabled()) {
            logger.info("Unregister: " + url);
        }
        registered.remove(url);
    }
    @Override
    public void subscribe(URL url, NotifyListener listener) {
        if (url == null) {
            throw new IllegalArgumentException("subscribe url == null");
        }
        if (listener == null) {
            throw new IllegalArgumentException("subscribe listener == null");
        }
        if (logger.isInfoEnabled()) {
            logger.info("Subscribe: " + url);
        }
        Set<NotifyListener> listeners = subscribed.computeIfAbsent(url, n -> new ConcurrentHashSet<>());
        listeners.add(listener);
    }
    @Override
    public void unsubscribe(URL url, NotifyListener listener) {
        if (url == null) {
            throw new IllegalArgumentException("unsubscribe url == null");
        }