Any method that is annotated with the @OnShutdown annotation will be called when NiFi is successfully shut down. If such a method throws an Exception, a log message will be generated, and the Exception will be otherwise ignored and other methods with this annotation will still be invoked. Methods with this annotation must take zero arguments. Note: while NiFi will attempt to invoke methods with this annotation on all components that use it, this is not always possible. For example, the process may be killed unexpectedly, in which case it does not have a chance to invoke these methods. Therefore, while methods using this annotation can be used to clean up resources, for instance, they should not be relied upon for critical business logic.