在启动含有 swagger 的 Spring Boot 项目时,可能会出现以下报错:

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2021-12-19 17:40:46.078  INFO 2848 --- [           main] d.s.w.p.DocumentationPluginsBootstrapper : Found 1 custom documentation plugin(s)
2021-12-19 17:40:46.081 WARN 2848 --- [ main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException
2021-12-19 17:40:46.302 INFO 2848 --- [ main] o.apache.catalina.core.StandardService : Stopping service [Tomcat]
2021-12-19 17:40:46.314 INFO 2848 --- [ main] ConditionEvaluationReportLoggingListener :

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-12-19 17:40:46.331 ERROR 2848 --- [ 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-5.3.13.jar:5.3.13]
at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.13.jar:5.3.13]
at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.13.jar:5.3.13]
at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.13.jar:5.3.13]
at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.13.jar:5.3.13]
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.13.jar:5.3.13]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.13.jar:5.3.13]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.1.jar:2.6.1]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:730) ~[spring-boot-2.6.1.jar:2.6.1]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412) ~[spring-boot-2.6.1.jar:2.6.1]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:302) ~[spring-boot-2.6.1.jar:2.6.1]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.1.jar:2.6.1]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1290) ~[spring-boot-2.6.1.jar:2.6.1]
at com.pikanglong.dataservice.DataApplication.main(DataApplication.java:12) ~[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.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:1441) ~[na:na]
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-5.3.13.jar:5.3.13]
... 14 common frames omitted


Process finished with exit code 1

原因是 swagger 和 Spring Boot 的版本不匹配。我当前使用的是 swagger 2.9.2 版本,最新的 Spring Boot 版本为 2.6.1。经过测试,swagger 2.9.2 最高支持到 Spring Boot 2.5.7(2.5 的最后一个小版本),2.6.0 及以上不兼容,在 pom 文件中将 Spring Boot 降级即可。

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<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.5.7</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>