Swagger is not working with Spring Boot 2.6.X

BySuresh Gadupu Spring Boot

In my previous blog post I have covered the topic of generating REST API documentation using swagger in Spring Boot application.

In my code I have used Spring Boot version 2.7.0, I did not face any issues but If I use Spring Boot version 2.6.x with Swagger I was getting below error when I start the application.

org.springframework.context.ApplicationContextException: Failed to start bean ‘documentationPluginsBootstrapper’

org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.20.jar:5.3.20]
	at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.8.jar:2.6.8]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:745) ~[spring-boot-2.6.8.jar:2.6.8]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:420) ~[spring-boot-2.6.8.jar:2.6.8]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) ~[spring-boot-2.6.8.jar:2.6.8]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1317) ~[spring-boot-2.6.8.jar:2.6.8]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.6.8.jar:2.6.8]
	at dev.fullstackcode.eis.SbSwaggerIntegrationApplication.main(SbSwaggerIntegrationApplication.java:34) ~[classes/:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[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:566) ~[na:na]
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.6.8.jar:2.6.8]
Caused by: java.lang.NullPointerException: null
	at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56) ~[springfox-spring-webmvc-3.0.0.jar:3.0.0]
	at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:113) ~[springfox-core-3.0.0.jar:3.0.0]
	at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89) ~[springfox-spi-3.0.0.jar:3.0.0]
	at java.base/java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469) ~[na:na]
	at java.base/java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[na:na]
	at java.base/java.util.TimSort.sort(TimSort.java:220) ~[na:na]
	at java.base/java.util.Arrays.sort(Arrays.java:1515) ~[na:na]
	at java.base/java.util.ArrayList.sort(ArrayList.java:1750) ~[na:na]
	at java.base/java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:392) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[na:na]
	at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81) ~[springfox-spring-webmvc-3.0.0.jar:3.0.0]
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) ~[na:na]
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[na:na]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.withDefaults(AbstractDocumentationPluginsBootstrapper.java:107) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.buildContext(AbstractDocumentationPluginsBootstrapper.java:91) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.bootstrapDocumentationPlugins(AbstractDocumentationPluginsBootstrapper.java:82) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:100) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.20.jar:5.3.20]Code language: Java (java)

If you are facing similar issue , you can use one of the following option to resolve it.

Solution I)

Add following property to application.properties

spring.mvc.pathmatch.matching-strategy=ant_path_matcherCode language: Java (java)

Then you can add bean process to Swagger config class.

@Configuration
@EnableSwagger2
public class SwaggerConfig {
    
    @Bean
    public Docket api() {
        return new Docket(DocumentationType.SWAGGER_2)
                .select()
                .apis(RequestHandlerSelectors.any())
                .paths(PathSelectors.any())
                .build();
    }

    @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);
                }
            }
        };
    }

}
Code language: Java (java)

Solution II )

Add bean process to Swagger config class.

@Configuration
@EnableSwagger2
public class SwaggerConfig {

    @Bean
    public Docket api() {
        return new Docket(DocumentationType.SWAGGER_2)
                .select()
                .apis(RequestHandlerSelectors.any())
                .paths(PathSelectors.any())
                .build();
    }

    @Bean
    public InitializingBean removeSpringfoxHandlerProvider(DocumentationPluginsBootstrapper bootstrapper) {
        return () -> bootstrapper.getHandlerProviders().removeIf(WebMvcRequestHandlerProvider.class::isInstance);
    }

    @Bean
    public RequestHandlerProvider customRequestHandlerProvider(Optional<ServletContext> servletContext, HandlerMethodResolver methodResolver, List<RequestMappingInfoHandlerMapping> handlerMappings) {
        String contextPath = servletContext.map(ServletContext::getContextPath).orElse(Paths.ROOT);
        return () -> handlerMappings.stream()
                .filter(mapping -> !mapping.getClass().getSimpleName().equals("IntegrationRequestMappingHandlerMapping"))
                .map(mapping -> mapping.getHandlerMethods().entrySet())
                .flatMap(Set::stream)
                .map(entry -> new WebMvcRequestHandler(contextPath, methodResolver, tweakInfo(entry.getKey()), entry.getValue()))
                .sorted(byPatternsCondition())
                .collect(toList());
    }

    RequestMappingInfo tweakInfo(RequestMappingInfo info) {
        if (info.getPathPatternsCondition() == null) return info;
        String[] patterns = info.getPathPatternsCondition().getPatternValues().toArray(String[]::new);
        return info.mutate().options(new RequestMappingInfo.BuilderConfiguration()).paths(patterns).build();
    }

Code language: Java (java)

Solution III

Add the actuator dependency

     <dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>Code language: HTML, XML (xml)

add following property to application.properties

spring.mvc.pathmatch.matching-strategy=ant_path_matcher

@Configuration
@EnableSwagger2
public class SwaggerConfig {

    @Bean
    public Docket api() {
        return new Docket(DocumentationType.SWAGGER_2)
                .select()
                .apis(RequestHandlerSelectors.any())
                .paths(PathSelectors.any())
                .build();
    }

    	@Bean
	public WebMvcEndpointHandlerMapping webEndpointServletHandlerMapping(WebEndpointsSupplier webEndpointsSupplier, ServletEndpointsSupplier servletEndpointsSupplier, ControllerEndpointsSupplier controllerEndpointsSupplier, EndpointMediaTypes endpointMediaTypes, CorsEndpointProperties corsProperties, WebEndpointProperties webEndpointProperties, Environment environment) {
		List<ExposableEndpoint<?>> allEndpoints = new ArrayList();
		Collection<ExposableWebEndpoint> webEndpoints = webEndpointsSupplier.getEndpoints();
		allEndpoints.addAll(webEndpoints);
		allEndpoints.addAll(servletEndpointsSupplier.getEndpoints());
		allEndpoints.addAll(controllerEndpointsSupplier.getEndpoints());
		String basePath = webEndpointProperties.getBasePath();
		EndpointMapping endpointMapping = new EndpointMapping(basePath);
		boolean shouldRegisterLinksMapping = this.shouldRegisterLinksMapping(webEndpointProperties, environment, basePath);
		return new WebMvcEndpointHandlerMapping(endpointMapping, webEndpoints, endpointMediaTypes, corsProperties.toCorsConfiguration(), new EndpointLinksResolver(allEndpoints, basePath), shouldRegisterLinksMapping, null);
	}


	private boolean shouldRegisterLinksMapping(WebEndpointProperties webEndpointProperties, Environment environment, String basePath) {
		return webEndpointProperties.getDiscovery().isEnabled() && (StringUtils.hasText(basePath) || ManagementPortType.get(environment).equals(ManagementPortType.DIFFERENT));
	}
}Code language: Java (java)

References

https://github.com/springfox/springfox/issues/3462

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Spring Boot – Generate REST API Documentation with Swagger

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