Spring Boot 2.6 以上整合 Swagger + Knife4j 报错

报错信息

org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException: Cannot invoke "org.springframework.web.servlet.mvc.condition.PatternsRequestCondition.getPatterns()" because "this.condition" is null
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.21.jar:5.3.21]
	at java.lang.Iterable.forEach(Iterable.java:75) ~[?:?]
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.21.jar:5.3.21]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.1.jar:2.7.1]
	at org.algotithmcontestdatacollect.displaybackend.DisplaybackendApplication.main(DisplaybackendApplication.java:9) ~[classes/:?]
Caused by: java.lang.NullPointerException: Cannot invoke "org.springframework.web.servlet.mvc.condition.PatternsRequestCondition.getPatterns()" because "this.condition" is null
	at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56) ~[springfox-spring-webmvc-2.10.5.jar:null]
	at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:112) ~[springfox-core-2.10.5.jar:null]
	at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89) ~[springfox-spi-2.10.5.jar:null]
	at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469) ~[?:?]
	at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[?:?]
	at java.util.TimSort.sort(TimSort.java:234) ~[?:?]
	at java.util.Arrays.sort(Arrays.java:1306) ~[?:?]
	at java.util.ArrayList.sort(ArrayList.java:1721) ~[?:?]
	at java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:392) ~[?:?]
	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:485) ~[?:?]
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[?:?]
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[?:?]
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:?]
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[?:?]
	at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:76) ~[springfox-spring-webmvc-2.10.5.jar:null]
	at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) ~[?:?]
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[?:?]
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[?:?]
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[?:?]
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[?:?]
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:?]
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[?:?]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.defaultContextBuilder(AbstractDocumentationPluginsBootstrapper.java:108) ~[springfox-spring-web-2.10.5.jar:null]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.buildContext(AbstractDocumentationPluginsBootstrapper.java:92) ~[springfox-spring-web-2.10.5.jar:null]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.bootstrapDocumentationPlugins(AbstractDocumentationPluginsBootstrapper.java:83) ~[springfox-spring-web-2.10.5.jar:null]
	at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:94) ~[springfox-spring-web-2.10.5.jar:null]
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.21.jar:5.3.21]
	... 14 more

报错原因

这个问题主要出现在 Spring Boot 2.6 及以后，只要是 Spring Boot 2.6 引入的新 PathPatternParser 导致的。

解决办法

两种解决办法

1. Path匹配策略切换回 ??ant_path_matcher ?

spring.mvc.pathmatch.matching-strategy=ant_path_matcher

2. 添加下面这个Bean的定义

@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));
}