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The service returned from the context will correspond with the implementation that was configured in the NiFi user interface. Configuring ControllerServices through the user interface is described in detail in the user guide.
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.
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