springboot和swagger2冲突及Swagger-ui/index.html界面404错误解决办法
swagger依赖：
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger2</artifactId>
<version>2.9.2</version>
</dependency>
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger-ui</artifactId>
<version>2.9.2</version>
</dependency>
报错信息：
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-12-22 21:53:13.203 ERROR 29012 --- [ 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) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.14.jar:5.3.14]
at java.lang.Iterable.forEach(Iterable.java:75) ~[na:1.8.0_311]
at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.14.jar:5.3.14]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.2.jar:2.6.2]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:730) [spring-boot-2.6.2.jar:2.6.2]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412) [spring-boot-2.6.2.jar:2.6.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:302) [spring-boot-2.6.2.jar:2.6.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) [spring-boot-2.6.2.jar:2.6.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1290) [spring-boot-2.6.2.jar:2.6.2]
at com.lin.swagger.SwaggerDemoApplication.main(SwaggerDemoApplication.java:13) [classes/:na]
Caused by: java.lang.NullPointerException: null
at springfox.documentation.spi.service.contexts.Orderings$8.compare(Orderings.java:112) ~[springfox-spi-2.9.2.jar:null]
at springfox.documentation.spi.service.contexts.Orderings$8.compare(Orderings.java:109) ~[springfox-spi-2.9.2.jar:null]
at com.google.common.collect.ComparatorOrdering.compare(ComparatorOrdering.java:37) ~[guava-20.0.jar:na]
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[na:1.8.0_311]
at java.util.TimSort.sort(TimSort.java:220) ~[na:1.8.0_311]
at java.util.Arrays.sort(Arrays.java:1438) ~[na:1.8.0_311]
at com.google.common.collect.Ordering.sortedCopy(Ordering.java:855) ~[guava-20.0.jar:na]
at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:57) ~[springfox-spring-web-2.9.2.jar:null]
at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:138) ~[springfox-spring-web-2.9.2.jar:null]
at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper$2.apply(DocumentationPluginsBootstrapper.java:135) ~[springfox-spring-web-2.9.2.jar:null]
at com.google.common.collect.Iterators$7.transform(Iterators.java:750) ~[guava-20.0.jar:na]
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) ~[guava-20.0.jar:na]
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) ~[guava-20.0.jar:na]
at com.google.common.collect.MultitransformedIterator.hasNext(MultitransformedIterator.java:52) ~[guava-20.0.jar:na]
at com.google.common.collect.MultitransformedIterator.hasNext(MultitransformedIterator.java:50) ~[guava-20.0.jar:na]
at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:249) ~[guava-20.0.jar:na]
at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:209) ~[guava-20.0.jar:na]
at com.google.common.collect.FluentIterable.toList(FluentIterable.java:614) ~[guava-20.0.jar:na]
at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.defaultContextBuilder(DocumentationPluginsBootstrapper.java:111) ~[springfox-spring-web-2.9.2.jar:null]
at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.buildContext(DocumentationPluginsBootstrapper.java:96) ~[springfox-spring-web-2.9.2.jar:null]
at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:167) ~[springfox-spring-web-2.9.2.jar:null]
at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.14.jar:5.3.14]
... 14 common frames omitted
原因是在springboot2.6.0中将SpringMVC 默认路径匹配策略从AntPathMatcher 更改为PathPatternParser，导致出错。（java项目fhadmin.cn）
可以在启动类上加上@EnableWebMvc注解或者在配置中切换为原先的AntPathMatcher
spring.mvc.pathmatch.matching-strategy=ant_path_matcher
加上以上配置后启动就不报错了，但是访问http://localhost:8080/swagger-ui/index.html报404
解决办法：把原来的swagger2和swagger-ui删掉，改成spring-boot-starter依赖
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
就可以正常访问了。
