...
In addition to the ControllerServices that come with Apache NiFi, alternate implementations, or additional services, can be developed by providing a custom NAR with an implementation of the given service. After deploying the NAR and restarting NiFi, the new implementation would be available from the NiFi user interface.
The nifi-standard-services module contains the shared APIs that can be leveraged. Browsing this module can provide the groupId, artifactId, and version of the various APIs.
...