Annotation-based event listener does not receive event published in @PostConstruct [SPR-15122]

[spring-projects-issues]

František Hartman opened SPR-15122 and commented

Annotation-based event listener does not receive event published in @PostConstruct, while old style interface based listener does.

See example project at https://github.com/frant-hartm/spring-application-events

One event is published in @PostConstruct method of another bean. Another event is published from main method after context is initialised. Interface based listener sees both events, annotation based sees only the second one:

Interface based sees event: MyEvent{value='from postConstruct'}
Annotation based sees event: MyEvent{value='from main'}
Interface based sees event: MyEvent{value='from main'}

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Affects: 4.3.5

Reference URL: https://github.com/frant-hartm/spring-application-events

Issue Links:

• ApplicationListener-like annotation for consuming application events [SPR-11622] #16245 ApplicationListener-like annotation for consuming application events
• Revisit "ApplicationEventMulticaster not initialized" behavior for early event publication scenarios [SPR-12902] #17501 Revisit "ApplicationEventMulticaster not initialized" behavior for early event publication scenarios
• Introduce API to select application listeners [SPR-15441] #20002 Introduce API to select application listeners

[snicoll]

The reason for this is that EventListenerMethodProcessor is a SmartInitializingSingleton that loops over beans in the context to determine if they have an annotated method in the afterSingletonsInstantiated phase. This essentially means that the listener is not registered (yet) in the PostConstruct phase of any bean.

IMO it is better this way as it makes things a bit more clear in terms of contracts. The annotation-based use case purely works by accident. If MyBean was processed before AnnotationBasedListener, it would not see the event either.