LoggingEventHookProvider
The LoggingEventHookProvider logs a string representation of each event using an SLF4J logger. The logger can be configured via NiFi Registry's logback.xml, which by default contains an appender that writes to a log file named nifi-registry-event.log in the logs directory.
<eventHookProvider>
<class>
org.apache.nifi.registry.provider.hook.LoggingEventHookProvider
</class>
</eventHookProvider>