【少见多怪志】Spring Boot 2.7 + Spring Boot Actuator + Swagger 的冲突问题

升级Spring boot到2.7之后，启动的时候遇到Swagger的报错问题:

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

遍查网络后发现所谓的解决，都是特定的局限场景：要么是没有使用spring boot actuator,  要么是没解决swagger-ui打开的问题。兼顾上面完整诉求的关键步骤如下。

1. springfox直接用最新版3.0.0，直接使用 `springfox-boot-starter` 不然不会有ui对应的mapping。注意mapping的路径为/swagger-ui/，不是swagger-ui.html

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId> <!-- 自动注册 /swagger-ui/ 的路由 -->
            <version>3.0.0</version>
        </dependency>

2. 配置mvc的path match策略为“ANT_PATH_MATCHER”：

  spring:
    mvc:
      pathmatch:
        matching-strategy: ANT_PATH_MATCHER

3. （最复杂的一步，不使用actuator的不需要）配置spring-boot-actuator的路径策略，注册HandlerMapping：

    @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));
    }