How to disable a particular event handler from axon?

Question

We have a few event handlers configured in the code. But, I'd like to disable a particular event handler from axon.

Please note - I can do this using @Profile or @Conditional parameter. But, I am interested to know if there is any way like config at EventConfig to exclude the particular event handler from processing.

Please refer below code.

Event Source Config

public class AxonConfig {
   
    public void configureProcessorDefault(EventProcessingConfigurer processingConfigurer) {
        processingConfigurer.usingSubscribingEventProcessors();
    }
}

Event handlers

@ProcessingGroup("this")
class ThisEventHandler {
    // your event handlers here...
}

@ProcessingGroup("that")
class ThatEventHandler {
    // your event handlers here...
}

@ProcessingGroup("other")
class OtherEventHandler {
    // your event handlers here...
}```

Answer 1

The EventProcessingConfiguration that's constructed as a result of the EventProcessingConfigurer provides a means to retrieve your Event Processor instances. Furthermore, any EventProcessor implementation has a start() and shutDown() method.

You can thus stop the Event Processors that you want to stop.

The following piece of code would get that done for you:

class EventProcessorControl {

    private final EventProcessingConfiguration processingConfig;

    EventProcessorControl(EventProcessingConfiguration processingConfig) {
        this.processingConfig = processingConfig;
    }

    public void startProcessor(String processorName) {
        processingConfig.eventProcessor(processorName)
                        .ifPresent(EventProcessor::start);
    }

    public void stopProcessor(String processorName) {
        processingConfig.eventProcessor(processorName)
                        .ifPresent(EventProcessor::shutDown);
    }
}

As a side note, I would warn against only using the SubscribingEventProcessor. Of the Event Processor implementations, it provides the least amount of flexibility when it comes to performance, distribution and error handling. I'd much rather try using the PooledStreamingEventProcessor instead.