当升级到Springboot 2.6.0 以上的版本后，Swagger 就不能正常工作了, 启动时报如下错误。当然如果你再使用sping boot Actuator 和 Springfox, 也会引起相关的NPE error. (github issue: https://github.com/springfox/springfox/issues/3462)

NFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: Caused by: org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at java.lang.Iterable.forEach(Iterable.java:75)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: at com.ebay.adscollection.app.AdstrackingcollectionApplication.main(AdstrackingcollectionApplication.java:12)
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: ... 14 more
INFO | jvm 1 | 2022/04/27 21:47:05 | WrapperJarApp: Caused by: java.lang.NullPointerException

下面就一一说明怎么解决

路径匹配策略

报错原因：
springboot2.6.0中将SpringMVC 默认路径匹配策略从AntPathMatcher 更改为PathPatternParser，导致出错

解决：
在 application.properties 文件中指定spring.mvc.pathmatch.matching-strategy=ant_path_matcher

Actuator

在Springboot 2.6 里Actuator 指定了ant_path_matcher，并且没有办法通过配置的方式来切换。我们可以通过定义bean 的方式来实现强制mapping。

@Bean
public WebMvcEndpointHandlerMapping webEndpointServletHandlerMapping(WebEndpointsSupplier webEndpointsSupplier, ServletEndpointsSupplier servletEndpointsSupplier, ControllerEndpointsSupplier controllerEndpointsSupplier, EndpointMediaTypes endpointMediaTypes, CorsEndpointProperties corsProperties, WebEndpointProperties webEndpointProperties, Environment environment) {
    List> allEndpoints = new ArrayList();
    Collection 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));
}

springfox

Springfox-swagger2:jar:3.0.0 在 spring boot 2.6.x不在支持，而是转向springdoc
因此就在springboot 2.6.x , spring doc 应该去掉，而是用 springdoc-openapi-ui 替换。

   
      org.springdoc
      springdoc-openapi-ui
      1.6.8

替换掉 swagger 2 annotations ，选用wagger 3 annotations wagger 3 annotations 报名是 io.swagger.v3.oas.annotations.

@Api → @Tag

@ApiIgnore → @Parameter(hidden = true) or @Operation(hidden = true) or @Hidden

@ApiImplicitParam → @Parameter

@ApiImplicitParams → @Parameters

@ApiModel → @Schema

@ApiModelProperty(hidden = true) → @Schema(accessMode = READ_ONLY)

@ApiModelProperty → @Schema

@ApiOperation(value = "foo", notes = "bar") → @Operation(summary = "foo", description = "bar")

@ApiParam → @Parameter

@ApiResponse(code = 404, message = "foo") → @ApiResponse(responseCode = "404", description = "foo")

如果你在application 里，不是用springfox 的dependency，而是自己定义多个Docket

@Bean
  public Docket publicApi() {
      return new Docket(DocumentationType.SWAGGER_2)
              .select()
              .apis(RequestHandlerSelectors.basePackage("org.github.springshop.web.public"))
              .paths(PathSelectors.regex("/public.*"))
              .build()
              .groupName("springshop-public")
              .apiInfo(apiInfo());
  }

  @Bean
  public Docket adminApi() {
      return new Docket(DocumentationType.SWAGGER_2)
              .select()
              .apis(RequestHandlerSelectors.basePackage("org.github.springshop.web.admin"))
              .paths(PathSelectors.regex("/admin.*"))
              .apis(RequestHandlerSelectors.withMethodAnnotation(Admin.class))
              .build()
              .groupName("springshop-admin")
              .apiInfo(apiInfo());
  }

那么就要改成

@Bean
  public GroupedOpenApi publicApi() {
      return GroupedOpenApi.builder()
              .group("springshop-public")
              .pathsToMatch("/public/**")
              .build();
  }
  @Bean
  public GroupedOpenApi adminApi() {
      return GroupedOpenApi.builder()
              .group("springshop-admin")
              .pathsToMatch("/admin/**")
              .addMethodFilter(method -> method.isAnnotationPresent(Admin.class))
              .build();
  }

如果只有一个Docket, 则要改成如下，用OpenAPI 而不是GroupedOpenApi

@Bean
  public OpenAPI springShopOpenAPI() {
      return new OpenAPI()
              .info(new Info().title("SpringShop API")
              .description("Spring shop sample application")
              .version("v0.0.1")
              .license(new License().name("Apache 2.0").url("http://springdoc.org")))
              .externalDocs(new ExternalDocumentation()
              .description("SpringShop Wiki Documentation")
              .url("https://springshop.wiki.github.org/docs"));
  }

同时设置参数在spring.factories 文件

springdoc.packagesToScan=package1, package2
springdoc.pathsToMatch=/v1, /api/balance/**

其他

If the swagger-ui is served behind a proxy:

how-can-i-deploy-springdoc-openapi-ui-behind-a-reverse-proxy

To customise the Swagger UI:

how-can-i-configure-swagger-ui

To hide an operation or a controller from documentation:

how-can-i-hide-an-operation-or-a-controller-from-documentation

refer link:

springboot 2.6 release note: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.6-Release-Notes#pathpattern-based-path-matching-strategy-for-spring-mvc
migrate to springDoc: https://springdoc.org/#migrating-from-springfox
spingfox github issue: https://github.com/springfox/springfox/issues/3791
stackoverflow post: https://stackoverflow.com/questions/70036953/springboot-2-6-0-spring-fox-3-failed-to-start-bean-documentationpluginsboot

Springboot 升级带来的Swagger异常

路径匹配策略

Actuator

springfox

其他

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