DocCollectionWatcher (Solr 9.1.1 solrj-zookeeper API)

```
public interface DocCollectionWatcher
```
Callback registered with ZkStateReader.registerDocCollectionWatcher(String, DocCollectionWatcher) and called whenever the DocCollection changes.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`boolean`	`onStateChanged(org.apache.solr.common.cloud.DocCollection collection)`	Called when the collection we are registered against has a change of state.

- Method Detail
  - onStateChanged
```
boolean onStateChanged(org.apache.solr.common.cloud.DocCollection collection)
```
    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.
    
    Parameters:
    
    collection - the new collection state (may be null if the collection has been deleted)
    
    Returns:
    
    true if the watcher should be removed