Axon Spring Boot application fails to start when multiple EventUpcasterChain spring beans are defined

Basic information

• Axon Framework version: 4.6.1
• JDK version: 17
• Complete executable reproducer if available (e.g. GitHub Repo): See attached project zip.

Steps to reproduce

Unzip the attached project and run: ./gradlew bootRun

Expected behaviour

The application is expected to start successfully.

Actual behaviour

The application fails to startup throwing this exception:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'eventStorageEngine' defined in class path resource [upcasterchaintest/AxonConfig.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.axonframework.eventsourcing.eventstore.EventStorageEngine]: Factory method 'eventStorageEngine' threw exception; nested exception is org.axonframework.common.AxonConfigurationException: Expected single candidate for component [EventUpcasterChain]. Found candidates: [eventUpcasterChain1, eventUpcasterChain2]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:658) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:638) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1352) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1195) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:955) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.23.jar:5.3.23]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.23.jar:5.3.23]
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.4.jar:2.7.4]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.4.jar:2.7.4]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.4.jar:2.7.4]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.4.jar:2.7.4]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.4.jar:2.7.4]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.4.jar:2.7.4]
        at upcasterchaintest.ApplicationKt.main(Application.kt:14) ~[main/:na]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.axonframework.eventsourcing.eventstore.EventStorageEngine]: Factory method 'eventStorageEngine' threw exception; nested exception is org.axonframework.common.AxonConfigurationException: Expected single candidate for component [EventUpcasterChain]. Found candidates: [eventUpcasterChain1, eventUpcasterChain2]
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.3.23.jar:5.3.23]
        at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.23.jar:5.3.23]
        ... 19 common frames omitted
Caused by: org.axonframework.common.AxonConfigurationException: Expected single candidate for component [EventUpcasterChain]. Found candidates: [eventUpcasterChain1, eventUpcasterChain2]
        at org.axonframework.spring.config.SpringConfigurer$ComponentLocator.findBean(SpringConfigurer.java:71) ~[axon-spring-4.6.1.jar:4.6.1]
        at org.axonframework.spring.config.SpringConfigurer.defaultComponent(SpringConfigurer.java:50) ~[axon-spring-4.6.1.jar:4.6.1]
        at org.axonframework.config.DefaultConfigurer.defaultUpcasterChain(DefaultConfigurer.java:523) ~[axon-configuration-4.6.1.jar:4.6.1]
        at org.axonframework.config.Component.get(Component.java:85) ~[axon-configuration-4.6.1.jar:4.6.1]
        at org.axonframework.config.DefaultConfigurer$ConfigurationImpl.upcasterChain(DefaultConfigurer.java:1021) ~[axon-configuration-4.6.1.jar:4.6.1]
        at upcasterchaintest.AxonConfig.eventStorageEngine(AxonConfig.kt:29) ~[main/:na]
        at upcasterchaintest.AxonConfig$$EnhancerBySpringCGLIB$$67064d7b.CGLIB$eventStorageEngine$0(<generated>) ~[main/:na]
        at upcasterchaintest.AxonConfig$$EnhancerBySpringCGLIB$$67064d7b$$FastClassBySpringCGLIB$$d63c1be1.invoke(<generated>) ~[main/:na]
        at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.3.23.jar:5.3.23]
        at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) ~[spring-context-5.3.23.jar:5.3.23]
        at upcasterchaintest.AxonConfig$$EnhancerBySpringCGLIB$$67064d7b.eventStorageEngine(<generated>) ~[main/:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na]
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.3.23.jar:5.3.23]
        ... 20 common frames omitted

However when removing 1 of the EventUpcasterChain beans defined in src/main/kotlin/upcasterchaintest/Upcasters.kt the application will start successfully.

upcasterchaintest.zip

[marnixrenne]

@smcvb Yes, I can confirm that all UpcasterChains were invoked during upcasting.

[marnixrenne]

@smcvb yes, this setup used to work prior to using the new Configuration API (instead, using the deprecated AxonConfiguration class). Currently we group our EventUpcasters per event type in an EventUpcasterChain and only these EventUpcasterChains are spring beans. From what I understand from the documentation this is a legitimate way to use Axon framework.

What I noticed when digging through the upcasterChain() call in the DefaultConfiguration class was that it was expecting a single bean of type EventUpcasterChain defined in the spring application context which was of course not the case.

For now we found a workaround by not using the Axon maven BOM, but explicitly specifying the versions in the dependencies. This probably changes the order in which spring components are loaded and works for us by coincidence, but this will not fix the example project included with this issue. So I still think it’s a bug, or subclassing EventUpcasterChain should be prohibited.