Swagger is not working with Spring Boot 2.6.X

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_matcher
Code 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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