public void watchDataChange(final String key,
                                final BiConsumer<String, String> updateHandler,
                                final Consumer<String> deleteHandler) {
        Watch.Listener listener = watch(updateHandler, deleteHandler);
        if (!watchCache.containsKey(key)) {
            Watch.Watcher watch = client.getWatchClient().watch(ByteSequence.from(key, UTF_8), listener);
            watchCache.put(key, watch);
        }
    }
subscribe data change.

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