解决方案之‘Failed to start bean ... nested exception is java.lang.NullPoi

‘documentationPluginsBootstrapper’; nested exception is java.lang.NullPointe

• • 1.1 Bug现场
  • 1.2 问题分析
  • 1.3 修复方案
  • • 1.3.1 修复方案一：降低Spring Boot 版本到2.6.x以下版本
    • 1.3.2 修复方案二: SpringBoot版本不降级解决方案
  • 1.4 参考资料

1.1 Bug现场

当Spring Boot 2.6.x 和Swagger 3.0.0 整合的时候，可能会报错如下所示：

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)
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54)
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356)
	at java.lang.Iterable.forEach(Iterable.java:75)
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155)
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123)
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
	at com.br.troubleshootquerytool.TroubleShootQueryToolApplication.main(TroubleShootQueryToolApplication.java:13)
Caused by: java.lang.NullPointerException: null
	at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56)
	at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:113)
	at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89)
	at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469)
	at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355)
	at java.util.TimSort.sort(TimSort.java:220)
	at java.util.Arrays.sort(Arrays.java:1512)
	at java.util.ArrayList.sort(ArrayList.java:1462)
	at java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:387)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
	at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81)
	at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.withDefaults(AbstractDocumentationPluginsBootstrapper.java:107)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.buildContext(AbstractDocumentationPluginsBootstrapper.java:91)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.bootstrapDocumentationPlugins(AbstractDocumentationPluginsBootstrapper.java:82)
	at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:100)
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178)
	... 14 common frames omitted

Process finished with exit code 1
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1.2 问题分析

因为Springfox 使用的路径匹配是基于AntPathMatcher的，而Spring Boot 2.6.X使用的是PathPatternMatcher。

1.3 修复方案

1.3.1 修复方案一：降低Spring Boot 版本到2.6.x以下版本

比如下面版本组合是兼容的

Spring Boot版本

Swagger 版本

2.5.6

2.9.2

1.3.2 修复方案二: SpringBoot版本不降级解决方案

比如下面版本组合是兼容的

Spring Boot版本

Swagger 版本

2.6.5

3.0.0

    
            io.springfox
            springfox-boot-starter
            3.0.0
    
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第一步:
application.yml 或applicaiton.properties 中添加如下配置

spring:
  mvc:
    pathmatch:
      matching-strategy: ant_path_matcher
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第二步:

项目中新建一个Java Config 类，内容如下：

/***
 * @author qingfeng.zhao
 * @date 2022/3/26
 * @apiNote
 */
@EnableOpenApi
@Configuration
public class SpringFoxSwaggerConfig {
    /**
     * 配置基本信息
     * @return
     */
    @Bean
    public ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("Swagger Test App Restful API")
                .description("swagger test app restful api")
                .termsOfServiceUrl("https://github.com/geekxingyun")
                .contact(new Contact("技术宅星云","https://xingyun.blog.csdn.net","fairy_xingyun@hotmail.com"))
                .version("1.0")
                .build();
    }

    /**
     * 配置文档生成最佳实践
     * @param apiInfo
     * @return
     */
    @Bean
    public Docket createRestApi(ApiInfo apiInfo) {
        return new Docket(DocumentationType.OAS_30)
                .apiInfo(apiInfo)
                .groupName("SwaggerGroupOneAPI")
                .select()
                .apis(RequestHandlerSelectors.withClassAnnotation(RestController.class))
                .paths(PathSelectors.any())
                .build();
    }

    /**
    * 增加如下配置可解决Spring Boot 6.x 与Swagger 3.0.0 不兼容问题
    **/
    @Bean
    public WebMvcEndpointHandlerMapping webEndpointServletHandlerMapping(WebEndpointsSupplier webEndpointsSupplier, ServletEndpointsSupplier servletEndpointsSupplier, ControllerEndpointsSupplier controllerEndpointsSupplier, EndpointMediaTypes endpointMediaTypes, CorsEndpointProperties corsProperties, WebEndpointProperties webEndpointProperties, Environment environment) {
        List> allEndpoints = new ArrayList();
        Collection 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));
    }
}
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1.4 参考资料

• https://github.com/springfox/springfox/issues/3462
• https://zhuanlan.zhihu.com/p/450064507
• https://mvnrepository.com/artifact/io.springfox/springfox-boot-starter/3.0.0