KafkaStreamsFunctionProcessor supports only one StreamsBuilderFactoryBeanConfigurer

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
java, kafka, spring, spring-boot
Domain
backend, stream-processing

Research direction

Start in KafkaStreamsBinderSupportAutoConfiguration.java around the KafkaStreamsFunctionProcessor at line 390, and inspect how getIfUnique obtains the StreamsBuilderFactoryBeanConfigurer. Reproduce the context with the custom configurer and the Spring Boot Kafka metrics configurer; done means both configurers are applied to the stream binding function rather than silently ignored.

Written by the indexing model from the issue text.

Description

The KafkaStreamsFunctionProcessor supports only a single StreamsBuilderFactoryBeanConfigurer.
Shouldn't it support a list of configurers?

The issue arose when upgrading to spring-boot-4.0.0 which has KafkaMetricsAutoConfiguration now in the spring-boot-kafka library.
My configurer was then silently ignored because getIfUnique returned null.

To Reproduce

  1. Consider a spring-boot-3.5.x project with a custom:
@Bean
public StreamsBuilderFactoryBeanConfigurer kafkaStreamsConfigurer() { ... }
  1. Upgrade to spring-boot-4.0.0
  2. Because of spring-kafka-4.0.0 a second StreamsBuilderFactoryBeanConfigurer will be in the context and both of them will be silently ignored now in the KafkaStreamsBinderSupportAutoConfiguration

Obviously this can easily be mitigated by adding @Primary to the custom Configurer if you don't care about the metrics like me.

Version of the framework
spring-cloud-2025.1.0
spring-boot-4.0.0

Expected behavior
Both Configurers are applied to the stream binding function.

Dominant language
Java
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Merged PRs (30d)
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