public interface CollectionStateWatcherCallback registered with
ZkStateReader.registerCollectionStateWatcher(String, CollectionStateWatcher)and called whenever the collection state changes.
boolean onStateChanged(Set<String> liveNodes, DocCollection collectionState)Called when the collection we are registered against has a change of state. Note that, due to the way Zookeeper watchers are implemented, a single call may be the result of several state changes. Also, multiple calls to this method can be made with the same state, ie. without any new updates.
liveNodes- the set of live nodes
collectionState- the new collection state (may be null if the collection has been deleted)
- true if the watcher should be removed