Kafka Streams auto-configuration should only configure default streams builder

[garyrussell]

KafkaStreamsAnnotationDrivenConfiguration

	@Bean
	public KafkaStreamsFactoryBeanConfigurer kafkaStreamsFactoryBeanConfigurer(
			StreamsBuilderFactoryBean factoryBean) {
		return new KafkaStreamsFactoryBeanConfigurer(this.properties, factoryBean);
	}

This blows up if there are multiple factory beans. Consider making it an ObjectProvider and getIfUnique() (or resolve in some other way).

2 people have reported this issue recently on Stack Overflow and today.

[snicoll]

Consider making it an ObjectProvider and getIfUnique()

@garyrussell looking at the conversation I am not sure sure about that. If someone creates their own bean, we should not apply our configuration to it so setting the autoStartup flag on the @Primary one feels wrong to me.

Looking at the discussion on the first post, it looks like they want to add something and still use the defaults provided by @EnableKafkaStreams. Regardless of wether we want to do that or not, we should not configure something that the user has configured IMO.

We already have a @ConditionalOnBean(name = KafkaStreamsDefaultConfiguration.DEFAULT_STREAMS_BUILDER_BEAN_NAME) at class level. I believe we should apply the same logic there.

[garyrussell]

@snicoll Makes sense; thanks for addressing it.

[vspiliopoulos]

Does this mean that if @EnableKafkaStreams is used, then only one factory (i.e. DEFAULT_STREAMS_BUILDER_BEAN_NAME) can be defined in the spring context? If not can you give an example context that loads with more than one factory (including the default one)?

Thanks!

[snicoll]

@vspiliopoulos as mentioned in the guidelines for contributing, we prefer to use GitHub issues only for bugs and enhancements and your question is not really related to the task at hand anyway. Let's keep the conversation in one place on your stackoverflow question.