[troubleshooting] 아직 명확한 해결법을 찾지 못한 Spring Boot web No ServletContext set 에러 현상

spring boot 2.3.0에서 아무것도 없이 빈 web을 띄울 때 아래 에러가 발생했다.

자체 구현한 autoConfigure 모듈을 사용한 아무것도 없는 빈 프로젝트 구축의 경우였다.

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'resourceHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.HandlerMapping]: Factory method 'resourceHandlerMapping' threw exception; nested exception is java.lang.IllegalStateException: No ServletContext set
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:656)
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:636)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:895)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
	at [mypackage].Application.main(Application.java:11)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.HandlerMapping]: Factory method 'resourceHandlerMapping' threw exception; nested exception is java.lang.IllegalStateException: No ServletContext set
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185)
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:651)
	... 18 common frames omitted
Caused by: java.lang.IllegalStateException: No ServletContext set
	at org.springframework.util.Assert.state(Assert.java:73)
	at org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport.resourceHandlerMapping(WebMvcConfigurationSupport.java:534)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
	... 19 common frames omitted

계속 debug를 하다 보니 대략의 원인은 AnnotationConfigServletWebServerApplicationContext를 생성하고 embeded tomcat을 생성하면 AnnotationConfigServletWebServerApplicationContext 클래스 변수로 tomcat의 ServletContext가 설정되고 그 이후 ServletContextAware를 구현한 빈들이 생성되면서 AnnotationConfigServletWebServerApplicationContext의 ServletContext를 사용하게 되는데 어찌 된 일인지 embeded tomcat 이 생성되기 전에 ServletContextAware를 구현한 빈들이 수행되면서 위와 같은 에러가 발생한 것이다.

정확한 발생 동기는 아직 찾지 못했다..

다만 해결이 되는 방법은 찾았는데 그게 왜 해결이 되는지는 찾지 못했다...

<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
</dependency>

위 참조를 하면 ValidationAutoConfiguration이 실행되고 해당 현상이 발생하지 않게 된다.

왜 이 현상이 발생했는지, 관련 이슈가 있는지 아직 찾지 못한 상태이다.

이런 경우를 겪어본 사람이 또 있는지 모르겠다.

---

2020-06-09 이 issue가 관련 있어 보인다.

https://github.com/spring-projects/spring-boot/issues/16936

Perform failure analysis of sliced tests that fail to bootstrap due to an IllegalStateException: No ServletContext set caused by