EventProcessingConfigurer should expose registered configurations

[nils-christian]

Hi,

In our application we want to use a custom EventProcessorBuilder. However, the builder is not able to access the event processor configurations registered at the EventProcessingConfigurer, making it difficult to correctly configure the new event processor.

Enhancement Description

Either the EventProcessingConfigurer should somehow expose the registered configurations via methods (compatible API change) or the EventProcessorBuilder should get the configuration of the event processor to build as parameter (incompatible API change).

Current Behaviour

Please take a look at the following code. Note that MyEventProcessorBuilder cannot access the previously registered configuration for MyEventProcessor.

@Autowired
void configure( final EventProcessingConfigurer configurer ) {
	// This code is usually somewhere else in the application.
	configurer.registerTrackingEventProcessorConfiguration( "MyEventProcessor", c -> TrackingEventProcessorConfiguration.forParallelProcessing( 4 ) );
}

@Autowired
void registerEventProcessorFactory( final EventProcessingConfigurer configurer ) {
	configurer.registerEventProcessorFactory( new MyEventProcessorBuilder( ) );
}

private static final class MyEventProcessorBuilder implements EventProcessorBuilder {

	@Override
	public EventProcessor build( final String name, final Configuration configuration, final EventHandlerInvoker eventHandlerInvoker ) {
		final List<EventProcessingModule> eventProcessingModules = configuration.findModules( EventProcessingModule.class );
		final EventProcessingModule eventProcessingModule = eventProcessingModules.get( 0 );
		@SuppressWarnings( "unchecked" )
		final StreamableMessageSource<TrackedEventMessage<?>> messageSource = ( StreamableMessageSource<TrackedEventMessage<?>> ) configuration.eventBus( );

		// In out application we are actually building a more specific event processor
		return TrackingEventProcessor
				.builder( )
				.name( name )
				.eventHandlerInvoker( eventHandlerInvoker )
				.rollbackConfiguration( eventProcessingModule.rollbackConfiguration( name ) )
				.errorHandler( eventProcessingModule.errorHandler( name ) )
				.messageMonitor( eventProcessingModule.messageMonitor( TrackingEventProcessor.class, name ) )
				.messageSource( messageSource )
				.tokenStore( eventProcessingModule.tokenStore( name ) )
				.transactionManager( eventProcessingModule.transactionManager( name ) )
				.trackingEventProcessorConfiguration(
						// TODO: We cannot access the configuration from the EventProcessingModule
						TrackingEventProcessorConfiguration.forParallelProcessing( 4 ) )
				.build( );
	}

}

Wanted Behaviour

private static final class MyEventProcessorBuilder implements EventProcessorBuilder {

		@Override
		public EventProcessor build( final String name, final Configuration configuration, final TrackingEventProcessorConfiguration tepConfiguration, final EventHandlerInvoker eventHandlerInvoker ) {
			final List<EventProcessingModule> eventProcessingModules = configuration.findModules( EventProcessingModule.class );
			final EventProcessingModule eventProcessingModule = eventProcessingModules.get( 0 );
			@SuppressWarnings( "unchecked" )
			final StreamableMessageSource<TrackedEventMessage<?>> messageSource = ( StreamableMessageSource<TrackedEventMessage<?>> ) configuration.eventBus( );

			// In out application we are actually building a more specific event processor
			return TrackingEventProcessor
					.builder( )
					.name( name )
					.eventHandlerInvoker( eventHandlerInvoker )
					.rollbackConfiguration( eventProcessingModule.rollbackConfiguration( name ) )
					.errorHandler( eventProcessingModule.errorHandler( name ) )
					.messageMonitor( eventProcessingModule.messageMonitor( TrackingEventProcessor.class, name ) )
					.messageSource( messageSource )
					.tokenStore( eventProcessingModule.tokenStore( name ) )
					.transactionManager( eventProcessingModule.transactionManager( name ) )
					.trackingEventProcessorConfiguration( tepConfiguration )
					.build( );
		}

	}

Possible Workarounds

Developing a custom EventProcessingConfigurer which delegates to the original EventProcessingConfigurer, just to store the configuration.

[smcvb]

Hi @nils-christian! Just to be clear here, the sole thing you're missing from the Configuration -> EventProcessingConfiguration is the TrackingEventProcessorConfiguration?
Or are there other components you'd need access to?

[nils-christian]

Hi @smcvb,

In our use case we are just missing the TrackingEventProcessorConfiguration, correct.

[smcvb]

Awesome, thanks! That should be simple enough to expose through the EventProcessingConfiguration, in a similar fashion as the other components.
I would expect the JavaDoc to specify the intent for it to be used within the EventProcessorBuilder, by the way.

Nonetheless, fair request here, @nils-christian 👍
Would you perhaps be up for a PR for this?
As it's a enhancement, it will be part of 4.7.0, by the way.
And I just want to add, we are not planning to withhold a release of 4.7.0 for as long as we did with 4.6.0. 😅