问题描述
SpringBoot项目中集成了knife4j，在将SpringBoot更新到2.6.0后启动项目异常：
Failed to start bean ‘documentationPluginsBootstrapper’; nested exception is java.lang.NullPointerException
异常堆栈信息如下：
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-12-23 16:52:35.735 ERROR 15348 --- [ main] 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)
at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54)
at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356)
at org.springframework.context.support.DefaultLifecycleProcessor$$Lambda$778/18341126.accept(Unknown Source)
at java.lang.Iterable.forEach(Iterable.java:75)
at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155)
at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123)
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:730)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:302)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1290)
at com.chqiuu.test.TestApplication.main(TestApplication.java:23)
Caused by: java.lang.NullPointerException: null
at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56)
at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:113)
at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89)
at springfox.documentation.spi.service.contexts.Orderings$$Lambda$796/7205235.apply(Unknown Source)
at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469)
at java.util.Comparator$$Lambda$68/3330950.compare(Unknown Source)
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:351)
at java.util.TimSort.sort(TimSort.java:230)
at java.util.Arrays.sort(Arrays.java:1512)
at java.util.ArrayList.sort(ArrayList.java:1454)
at java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:387)
at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:513)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81)
at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper$$Lambda$790/3038834.apply(Unknown Source)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
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)
... 15 common frames omitted
解决方案
这个问题困扰了我很久，也在网上找了好多资料，也有些人说springboot版本升级的导致的问题。
找到的解决办法有两种：
- 将springboot降级到2.5.7，但这也只是暂时解决问题的办法，不是长久之计。
- 从SpringFox迁移到SpringDoc，这种方式虽然可以处理问题，但对于已经上线的项目来说改动量还是有点大。
这上面两种解决方案都不是我最想要的。最近对Spring Boot 2.6.0的文档进行研究发现，2.6.0开始使用基于PathPatternParser的路径匹配，而Springfox版本一直没有更新还是使用的AntPathMatcher导致了这个问题。
要处理问题也很简单，修改yaml文件，将SpringBoot路劲匹配模式修改为AntPathMatcher就可以了，properties的配置如下：
spring.mvc.pathmatch.matching-strategy=ANT_PATH_MATCHER
修改application.yml文件配置：
spring:
mvc:
pathmatch:
matching-strategy: ANT_PATH_MATCHER