public String get(final String key) {
        CuratorCache cache = findFromCache(key);
        if (Objects.isNull(cache)) {
            return getDirectly(key);
        }
        ChildData data = cache.get(key).orElse(null);
        if (Objects.isNull(data)) {
            return getDirectly(key);
        }
        return Objects.isNull(data.getData()) ? null : new String(data.getData(), StandardCharsets.UTF_8);
    }
get value for specific key.

@param key zookeeper path
@return value.
shenyu-registry/shenyu-registry-zookeeper/src/main/java/org/apache/shenyu/registry/zookeeper/ZookeeperClient.java