public void watchChildChange(final String key,
                                 final BiConsumer<String, String> updateHandler,
                                 final Consumer<String> deleteHandler) {
        Watch.Listener listener = watch(updateHandler, deleteHandler);
        WatchOption option = WatchOption.newBuilder()
                .withPrefix(ByteSequence.from(key, UTF_8))
                .build();
        if (!watchChildCache.containsKey(key)) {
            Watch.Watcher watch = client.getWatchClient().watch(ByteSequence.from(key, UTF_8), option, listener);
            watchChildCache.put(key, watch);
        }
    }
subscribe sub node change.

@param key           param node name.
@param updateHandler sub node handler of update
@param deleteHandler sub node delete of delete
shenyu-sync-data-center/shenyu-sync-data-etcd/src/main/java/org/apache/shenyu/sync/data/etcd/EtcdClient.java