Provide a way to define a ContainerCustomizer per KafkaListener

[frosiere]

Following https://stackoverflow.com/questions/77193702/consumerrebalancelistener-and-or-containerproperties-override-per-container,

Through a new property on the KafkaListener annotation, it should be possible to specify the bean name of the ContainerCustomizer associated to the listener.

@KafkaListener(... containerCustomizer="myContainerCustomizerBeanName" ...)
void on(ConsumerRecords records) {
...

If provided, this customizer would override the default factory customizer.

See KafkaListenerAnnotationBeanPostProcessor and KafkaListenerEndpoint for internal details.

Would be great to have this feature on both Spring Kafka 2.9.x and 3.0.x

[garyrussell]

It is unlikely this would be back ported to versions earlier than the upcoming 3.1.

It's really just a convenience feature; the existing single customizer per factory has access to the container's listener id when performing customization.

[garyrussell]

Actually, this is not so straightforward; defining multiple beans will disable Boot's capability of auto configuring the default customizer. And, if you only define one bean, it will be detected by Boot and auto configure it into the factory.

We will probably have to use a different interface for this customizer.

[frosiere]

Good catch. Didn't see it on the 2.9.x as this configuration has been introduced on the 3.1.x (spring-projects/spring-boot#34033). Seems weird to not have used the ConcurrentKafkaListenerContainerFactoryConfigurer to set the customizer on the factory.

This may be confusing to introduce a new interface, but this seems the way to go...

[frosiere]

What about ContainerConfigurer? May it help if I drop a PR for that or do you prefer to implement it yourself?

[garyrussell]

The Boot team does not like us using *Configurer - that is their convention and it causes some confusion; it is unlikely that they will add one for this, but in the past we ended up with the same class name in Boot and the upstream project.

Happy to receive a PR, if we can come up with a name.

Maybe ContainerPostProcessor for the interface? (the attribute name can still be customizer; perhaps should be because we want this to be applied instead of the common customizer - and the Javadocs should explain that).

[frosiere]

Looks good to me. Will drop a PR this week. Thanks.