org.springframework.context.ApplicationContextException: Failed to start bean ‘documentationPluginsB

在使用Swagger2接口文档时 SpringBoot完整报错如下:

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-5.3.20.jar:5.3.20]
    at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.20.jar:5.3.20]
    at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.20.jar:5.3.20]
    at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
    at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.20.jar:5.3.20]
    at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.20.jar:5.3.20]
    at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.20.jar:5.3.20]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.20.jar:5.3.20]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.0.jar:2.7.0]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) [spring-boot-2.7.0.jar:2.7.0]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) [spring-boot-2.7.0.jar:2.7.0]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) [spring-boot-2.7.0.jar:2.7.0]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) [spring-boot-2.7.0.jar:2.7.0]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) [spring-boot-2.7.0.jar:2.7.0]
    at com.xxxx.server.YebApplication.main(YebApplication.java:18) [classes/:na]
Caused by: java.lang.NullPointerException: null
    at springfox.documentation.spi.service.contexts.Orderings$8.compare(Orderings.java:113) ~[springfox-spi-2.7.0.jar:2.7.0]
    at springfox.documentation.spi.service.contexts.Orderings$8.compare(Orderings.java:110) ~[springfox-spi-2.7.0.jar:2.7.0]
    at com.google.common.collect.ComparatorOrdering.compare(ComparatorOrdering.java:38) ~[guava-18.0.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:1440) ~[na:na]
    at com.google.common.collect.Ordering.sortedCopy(Ordering.java:817) ~[guava-18.0.jar:na]
    at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:52) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:129) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:126) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at com.google.common.collect.Iterators$8.transform(Iterators.java:799) ~[guava-18.0.jar:na]
    at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48) ~[guava-18.0.jar:na]
    at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48) ~[guava-18.0.jar:na]
    at com.google.common.collect.Iterators$5.hasNext(Iterators.java:548) ~[guava-18.0.jar:na]
    at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:268) ~[guava-18.0.jar:na]
    at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:226) ~[guava-18.0.jar:na]
    at com.google.common.collect.FluentIterable.toList(FluentIterable.java:373) ~[guava-18.0.jar:na]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.defaultContextBuilder(DocumentationPluginsBootstrapper.java:100) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.buildContext(DocumentationPluginsBootstrapper.java:91) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:154) ~[springfox-spring-web-2.7.0.jar:2.7.0]
    at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.20.jar:5.3.20]
    ... 14 common frames omitted

仔细检查后发现，原来时项目pom.xml中的Springboot版本太高导致的，我使用的是最新版本2.7.0

改成2.3.0.RELEASE版本就能正常启动项目了

    org.springframework.boot
    spring-boot-starter-parent
    2.3.0.RELEASE