springboot及swagger2整合报错：documentationPluginsBootstrapper

1. 先给出解决方案

如果英文好直接参考这篇文章：https://fullstackcode.dev/2022/06/12/swagger-is-not-working-with-spring-boot-2-6-x/，这是我尝试了网上多种解决方案无果之后，真正解决了问题的文章，当然作者参考的也是官方讨论组，详情过程可以查看：https://github.com/springfox/springfox/issues/3462。这里面也告诉我们一般出现插件问题，记得第一时间去查看开源项目里面的issues，一般你遇到的问题，大家都会遇到，尤其国外程序员一般都乐意分享，大多数时候都能找到答案。

我使用的是作者给到的第三种方案：

1. 添加actuator依赖：

<dependency>
   <groupId>org.springframework.bootgroupId>
    <artifactId>spring-boot-starter-actuatorartifactId>
dependency>

2. 修改Application.yml配置：

mvc:
    pathmatch:
      matching-strategy: ANT_PATH_MATCHER

如果是properties文件，配置如下：

spring.mvc.pathmatch.matching-strategy=ant_path_matcher

swagger配置文件添加关键方法：

@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));
    }
}

从代码来看，里面的核心方法webEndpointServletHandlerMapping，做了高版本的兼容，我估计在后面Swagger如果做更新的时候，应该会做一定的兼容性。

2.高版本整合出错及详细解决方案

以前使用Swagger版本的时候，都是一次性启动成功，但是这次将Springboot使用新版本之后，居然报错了，主要的错误信息如下：

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-5.3.23.jar:5.3.23]
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.23.jar:5.3.23]
	at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.4.jar:2.7.4]
	at stu.up2uper.springstu.SpringStuApplication.main(SpringStuApplication.java:14) ~[classes/:na]
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.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:1232) ~[na:na]
	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-5.3.23.jar:5.3.23]
	... 14 common frames omitted

我引用的相关包信息如下：

<parent>
    <groupId>org.springframework.bootgroupId>
    <artifactId>spring-boot-starter-parentartifactId>
    <version>2.7.4version>
    <relativePath/> 
parent>
<dependencies>
	<dependency>
      <groupId>io.springfoxgroupId>
       <artifactId>springfox-swagger2artifactId>
       <version>2.9.2version>
   dependency>
   <dependency>
       <groupId>io.springfoxgroupId>
       <artifactId>springfox-swagger-uiartifactId>
       <version>2.9.2version>
   dependency>
dependencies>

第一反应就是版本冲突不兼容导致的，百度了几种方案都无果，主要一下几种方案：

• 版本兼容法：降低springboot版本，使用配套swagger
• 更新Google Guava法：升级或者指定特定guava版本
• 修改注释法：添加@EnableWebMvc之类的注解之类来修改

@EnableAsync
@EnableWebMvc
@ServletComponentScan
@ComponentScan(basePackages = {"com.xmair.restapi","com.xmair.core.service"})
@MapperScan("com.xmair.core.mapper")
public class MFISRestAPIApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MFISRestAPIApplication.class, args);
    }
}

• 添加资源法：估计是无法获取swagger所需资源，而导致无法启动

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/**").addResourceLocations("classpath:/static/");
        registry.addResourceHandler("doc.html").addResourceLocations("classpath:/META-INF/resources/");
        registry.addResourceHandler("/webjars/**").addResourceLocations("classpath:/META-INF/resources/webjars/");
        registry.addResourceHandler("swagger-ui.html").addResourceLocations("classpath:/META-INF/resources/");
}

反正以上方案都没解决我的问题，可能上面方法在某些环境及版本之下是适用的，最终还是前面提到的方案解决了问题。方案三已在上方表述，下方把另外两种方案搬砖过来，给大家做参考：

方案一、修改配置及添加兼容代码
修改配置就是上面一样：

mvc:
    pathmatch:
      matching-strategy: ANT_PATH_MATCHER

如果是properties文件，配置如下：

spring.mvc.pathmatch.matching-strategy=ant_path_matcher

同时，修改核心代码：

@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);
                }
            }
        };
    }

}

方案二、修改swagger配置核心代码

@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();
    }
}

希望以上的方案能够帮助大家解决问题，同时通过这次解决问题，又一次验证了遇到开源项目错误的解决途径：

简单百度无果，一定要用Google，或者开源项目的讨论区。