What if no event handlers there?

In Axon4.2, what will happen if one event being send, and on event handlers being found?
while it retry for some times,and being ingnore? or replay at the first time a handler being found?
If anyone can help me with this question?

Hi Andrew,

The behaviour of actually handling the event, depends on the technical mechanism you choose to provide events to the Event Handlers you code.
This mechanism is called the Event Processor within Axon Framework, for which (currently) two implementations exist:

  1. SubscribingEventProcessor
  2. TrackingEventProcessor
    Option 1, the Subscribing Event Processor, is basically an event push mechanism, within a single JVM.
    Option 2 on the other hand is a pull mechanism, which thus retrieves events from the Event storage mechanism.

Having said this, if you would use Subscribing Event Processor throughout your application and you’ve missed adding an Event Handling function for a given event, then it would not be handled anymore.
However, if you switch to a Tracking Event Processor, the process of publishing an event and handling it are completely segregating from one another.
You could thus very easily add an Event Handler for an event at a latter stage and still have all your previous events handled.

Note that it’s the Tracking Event Processor which gives you the replayability within an Axon application.
If you are thus looking to replay query models at later stages, then you should use the Tracking Event Processor.
Lastly, within a default configured Axon application for version 4 and up, the default event processor is the Tracking Event Processor.

Hope this clarifies things for you Andrew!


Hi Steven,

Thank you for your patient reply. Your answer really clarifies things for me.


在 2019年9月4日星期三 UTC+8下午4:55:21,Steven van Beelen写道: