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.