[Spring Boot] Actuator dependency와 Swagger Starter 3.0.0 충돌 에러

Spring boot 2.7.3에서 Swagger 3.0.0 버전과 함께 Actuator dependency를 추가하는 과정에서 아래와 같은 오류가 발생했다. 

Swagger 3.0.0 dependency를 추가했던 과정에서 발생한 오류와 동일했다.

1. 문제 발생 🤬

Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException

porm.xml - Dependency

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>3.0.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

 

2. 문제 해결 😁

Swagger는 모든 endpoint에 대해 documentation을 해주는 기능이다. Actuator 또한 endpoint(refresh, beans, health) 등을 직접 생성하는 역할이다 보니 둘의 의존성이 충돌하게 된다.

Sprinfox는 Sprinf MVC가 Ant-based path matcher를 기본값으로 하여 경로를 찾는 것으로 가정하는데 Spring MVC 2.6.X부터 기본값을 Ant-based path matcher에서 PathPatter-based matcher로 변경하여 발생하는 버그이다.

해결 방법으로는 3가지가 있는데 나는 2번으로 해결하였다.

1. SpringBoot 버전을 2.5.x이하로 변경한다.
2. Ant-based path matcher으로 경로 변경 & springfoxHandlerProvider 추가
3. Springdoc 사용..

application.yml

spring:
  mvc:
    pathmatch:
      matching-strategy: ant_path_matcher

SwaggerConfig.java

@Configuration
@EnableSwagger2
public class SwaggerConfig {
 
 
    @Bean
    public static BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
        return new BeanPostProcessor() {
 
            @Override
            public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
                if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
                    customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
                }
                return bean;
            }
 
            private <T extends RequestMappingInfoHandlerMapping> void customizeSpringfoxHandlerMappings(List<T> mappings) {
                List<T> copy = mappings.stream()
                        .filter(mapping -> mapping.getPatternParser() == null)
                        .collect(Collectors.toList());
                mappings.clear();
                mappings.addAll(copy);
            }
 
            @SuppressWarnings("unchecked")
            private List<RequestMappingInfoHandlerMapping> getHandlerMappings(Object bean) {
                try {
                    Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
                    field.setAccessible(true);
                    return (List<RequestMappingInfoHandlerMapping>) field.get(bean);
                } catch (IllegalArgumentException | IllegalAccessException e) {
                    throw new IllegalStateException(e);
                }
            }
        };
    }
 
    // CONTACT
    private static final Contact DEFAULT_CONTACT = new Contact("Kenneth Lee", "http://www.joneconsulting.co.kr","edowon@joneconsulting.co.kr" );
 
    // API INFO
    private static final ApiInfo DEFAULT_API_INFO = new ApiInfo("Awesome API Title",
            "My User management REST API Service",
            "1.0",
            "urn:tos",
            DEFAULT_CONTACT,
            "Apache License Version 2.0",
            "http://www.apache.org/licenses/LICENSE-2.0",
            new ArrayList<>());
 
 
    // PRODUCES AND CONSUMES  --> application.yml
    private static final Set<String> DEFAULT_PRODUCES_AND_CONSUMES = new HashSet<>(
            Arrays.asList("application/json", "application/xml"));
 
    // localhost:8088/v2/api-docs
    @Bean
    public Docket DocumentApi(){
        return new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(DEFAULT_API_INFO)
                .produces(DEFAULT_PRODUCES_AND_CONSUMES)
                .consumes(DEFAULT_PRODUCES_AND_CONSUMES);
    }
 
}
 

이처럼 config에 springfoxHandlerProvider를 추가하니 문제를 해결했다!

@Bean
public static BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
    return new BeanPostProcessor() {
 
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
                customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
            }
            return bean;
        }
 
        private <T extends RequestMappingInfoHandlerMapping> void customizeSpringfoxHandlerMappings(List<T> mappings) {
            List<T> copy = mappings.stream()
                    .filter(mapping -> mapping.getPatternParser() == null)
                    .collect(Collectors.toList());
            mappings.clear();
            mappings.addAll(copy);
        }
 
        @SuppressWarnings("unchecked")
        private List<RequestMappingInfoHandlerMapping> getHandlerMappings(Object bean) {
            try {
                Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
                field.setAccessible(true);
                return (List<RequestMappingInfoHandlerMapping>) field.get(bean);
            } catch (IllegalArgumentException | IllegalAccessException e) {
                throw new IllegalStateException(e);
            }
        }
    };
}

요약 👉 Springboot 2.6.x 이상에서 swagger와 Acutator의 버전 호환성 문제가 발생하면

1) application.yml에  spring: mvc: pathmatch: matching-strategy: ant_path_matcher을 추가하고

2) springfoxHandlerProvider를 추가하자!

 

Reference

https://stackoverflow.com/questions/70589430/nullpointerexception-when-upgrading-spring-boot-to-version-2-6-2

NullPointerException when upgrading Spring Boot to version 2.6.2

https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/util/pattern/PathPattern.html

https://middleearth.tistory.com/69

https://dkswnkk.tistory.com/672

Spring actuator 의존성 추가만으로 nullpointerexception가 발생할때 해결방법