I am getting this error "Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException"

Question

I am continuously getting this error while adding configuration of swagger ui do help because I am stuck at this point. I already tried to add ant-path-matcher strategy but it doesn't work

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2022-05-24 11:07:48.532 ERROR 1624 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

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.lang.Iterable.forEach(Iterable.java:75) ~[na:1.8.0_333]
    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 com.wipro.gl.Library1Application.main(Library1Application.java:11) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_333]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_333]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_333]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_333]
    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.spi.service.contexts.Orderings$8.compare(Orderings.java:112) ~[springfox-spi-2.9.2.jar:null]
    at springfox.documentation.spi.service.contexts.Orderings$8.compare(Orderings.java:109) ~[springfox-spi-2.9.2.jar:null]
    at com.google.common.collect.ComparatorOrdering.compare(ComparatorOrdering.java:37) ~[guava-20.0.jar:na]
    at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[na:1.8.0_333]
    at java.util.TimSort.sort(TimSort.java:220) ~[na:1.8.0_333]
    at java.util.Arrays.sort(Arrays.java:1438) ~[na:1.8.0_333]
    at com.google.common.collect.Ordering.sortedCopy(Ordering.java:855) ~[guava-20.0.jar:na]
    at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:57) ~[springfox-spring-web-2.9.2.jar:null]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:138) ~[springfox-spring-web-2.9.2.jar:null]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:135) ~[springfox-spring-web-2.9.2.jar:null]
    at com.google.common.collect.Iterators$7.transform(Iterators.java:750) ~[guava-20.0.jar:na]
    at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) ~[guava-20.0.jar:na]
    at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) ~[guava-20.0.jar:na]
    at com.google.common.collect.MultitransformedIterator.hasNext(MultitransformedIterator.java:52) ~[guava-20.0.jar:na]
    at com.google.common.collect.MultitransformedIterator.hasNext(MultitransformedIterator.java:50) ~[guava-20.0.jar:na]
    at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:249) ~[guava-20.0.jar:na]
    at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:209) ~[guava-20.0.jar:na]
    at com.google.common.collect.FluentIterable.toList(FluentIterable.java:614) ~[guava-20.0.jar:na]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.defaultContextBuilder(DocumentationPluginsBootstrapper.java:111) ~[springfox-spring-web-2.9.2.jar:null]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.buildContext(DocumentationPluginsBootstrapper.java:96) ~[springfox-spring-web-2.9.2.jar:null]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:167) ~[springfox-spring-web-2.9.2.jar:null]
    at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.20.jar:5.3.20]
    ... 19 common frames omitted

Here is my pom file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.8</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.wipro.gl</groupId>
    <artifactId>Library1</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Library1</name>
    <description> Project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>2.9.2</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>2.9.2</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>

        </plugins>
    </build>

</project>

and here is my configuration file

@Configuration
@EnableSwagger2
public class springConfig {

    @Bean
    public Docket library() {
        return new Docket(DocumentationType.SWAGGER_2).groupName("Library").select()
                .apis(RequestHandlerSelectors.basePackage("com.wipro.gl.controller")).build();
    }

}

Answer 1

Looks like the latest spring-boot version 2.6.8 is incompatible with Swagger 2. I have faced the same issue and there are two workarounds.

1. Try downgrading your springboot version lower than 2.5.0 (Simple workaround).

2. Upgrade the swagger to OpenApi, which is likely to be called as Swagger3. This has few changes with the annotations. You can easily migrate from Swagger 2 to OpenApi 3 by following guides available on the internet.

Second workaround of upgrading swagger is preferable since the Swagger 2 from springfox is getting old and the last version was released on July 2020. OpenApi is the latest API specification.

Answer 2

I was facing the same issue but I was able to resolve the issue without downgrading the springboot version. I am using gradle and spring boot version 2.7.0

Just add @EnableWebMvc in the application class.

@SpringBootApplication
@EnableWebMvc
public class Application{
   public static void main(String [] args){
     SpringApplication.run(Application.class, args);
  }
}
 

Answer 3

If setting the below in application.properties doesnt work, spring.mvc.pathmatch.matching-strategy = ANT_PATH_MATCHER

workaround is to set the below annotations

@EnableWebMvc
@EnableSwagger2
@Component
public class SwaggersConfig {
}

Another workaround is to simply revert org.springframework.boot version to 2.5.X

Answer 4

github issue

This works for me.

@Configuration
public class SwaggerHandlerProviderBeanPostProcessor implements 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);
        }
    }
}

Answer 5

The answer takes a long time for me, but this works for me. https://github.com/springfox/springfox/issues/3462#issuecomment-1113915063

My version: Spring boot 2.7, swagger/springfox 3.0.0

@Configuration
@EnableKnife4j
@EnableOpenApi
public class Knife4jConfiguration {
    public Docket defaultApi() {...}
    private ApiInfo apiInfo() {...}

    // importantion: resolving imcompatibility
    @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));
    }
}