解决Failed to start bean ‘documentationPluginsBootstrapper‘； nested exception is java.lang.NullPointer

1. 背景

• 升级springboot版本从2.2到2.6.6后，同时使用swagger3，启动后报错
• Failed to start bean ‘documentationPluginsBootstrapper’; nested exception is java.lang.NullPointerException

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-5.3.18.jar:5.3.18]
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.18.jar:5.3.18]
	at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.6.jar:2.6.6]
	at com.example.demo.DemoApplication.main(DemoApplication.java:10) ~[classes/:na]

2. 问题原因

• https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.6-Release-Notes

• 在SpringBoot2.6之后，Spring MVC 处理程序映射匹配请求路径的默认策略已从 AntPathMatcher 更改为PathPatternParser。如果需要切换为AntPathMatcher，官方给出的方法是配置spring.mvc.pathmatch.matching-strategy=ant_path_matcher

• 但是actuator endpoints在2.6之后也使用基于 PathPattern 的 URL 匹配，而且actuator endpoints的路径匹配策略无法通过配置属性进行配置，如果同时使用Actuator和Springfox，会导致程序启动失败，所以只是进行上面的设置是不行的。

3. 解决办法

• 因为springfox在2020年7月之后就停止更新了，所以无法通过升级springfox版本解决；

方法一、修改配置

• 参考https://github.com/springfox/springfox/issues/3462#issuecomment-1010721223

1、依赖

• pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.6.6version>
        <relativePath/> 
    parent>
    <groupId>com.examplegroupId>
    <artifactId>demoartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>demoname>
    <description>demodescription>
    <properties>
        <java.version>11java.version>
    properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-actuator-autoconfigureartifactId>
        dependency>
        
        <dependency>
            <groupId>io.springfoxgroupId>
            <artifactId>springfox-boot-starterartifactId>
            <version>3.0.0version>
        dependency>

        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <optional>trueoptional>
        dependency>

    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombokgroupId>
                            <artifactId>lombokartifactId>
                        exclude>
                    excludes>
                configuration>
            plugin>
        plugins>
    build>

project>

2、在application.properties中设置

spring.mvc.pathmatch.matching-strategy=ant_path_matcher

3、在swagger配置类中添加以下代码

package com.example.demo.config;

import org.springframework.boot.actuate.autoconfigure.endpoint.web.CorsEndpointProperties;
import org.springframework.boot.actuate.autoconfigure.endpoint.web.WebEndpointProperties;
import org.springframework.boot.actuate.autoconfigure.web.server.ManagementPortType;
import org.springframework.boot.actuate.endpoint.ExposableEndpoint;
import org.springframework.boot.actuate.endpoint.web.EndpointLinksResolver;
import org.springframework.boot.actuate.endpoint.web.EndpointMapping;
import org.springframework.boot.actuate.endpoint.web.EndpointMediaTypes;
import org.springframework.boot.actuate.endpoint.web.ExposableWebEndpoint;
import org.springframework.boot.actuate.endpoint.web.WebEndpointsSupplier;
import org.springframework.boot.actuate.endpoint.web.annotation.ControllerEndpointsSupplier;
import org.springframework.boot.actuate.endpoint.web.annotation.ServletEndpointsSupplier;
import org.springframework.boot.actuate.endpoint.web.servlet.WebMvcEndpointHandlerMapping;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;
import org.springframework.util.StringUtils;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.oas.annotations.EnableOpenApi;
import springfox.documentation.service.ApiInfo;
import springfox.documentation.service.Contact;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * @ClassName: SwaggerConfig
 * @Description:
 * @Author: Fisher
 * @Date: 2022/4/20 1:34 PM
 **/
@Configuration
@EnableOpenApi
public class SwaggerConfig {

    @Bean
    public Docket restApi() {
        return new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(apiInfo())
                .useDefaultResponseMessages(true)
                .forCodeGeneration(false)
                .select()
                .apis(RequestHandlerSelectors.basePackage("com.example"))
                .paths(PathSelectors.any())
                .build();
    }

    private ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("title")
                .description("这里放描述")
                .contact(new Contact("Fisher", "https://blog.csdn.net/qq_40977118", "[email protected]"))
                .version("1.0")
                .build();
    }

    @Bean
    public WebMvcEndpointHandlerMapping webEndpointServletHandlerMapping(WebEndpointsSupplier webEndpointsSupplier,
        ServletEndpointsSupplier servletEndpointsSupplier, ControllerEndpointsSupplier controllerEndpointsSupplier,
        EndpointMediaTypes endpointMediaTypes, CorsEndpointProperties corsProperties,
        WebEndpointProperties webEndpointProperties, Environment environment) {
        List<ExposableEndpoint<?>> allEndpoints = new ArrayList<>();
        Collection<ExposableWebEndpoint> 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 =
            webEndpointProperties.getDiscovery().isEnabled() && (StringUtils.hasText(basePath)
                || ManagementPortType.get(environment).equals(ManagementPortType.DIFFERENT));
        return new WebMvcEndpointHandlerMapping(endpointMapping, webEndpoints, endpointMediaTypes,
            corsProperties.toCorsConfiguration(), new EndpointLinksResolver(allEndpoints, basePath),
            shouldRegisterLinksMapping, null);
    }

}

• 这个WebMvcEndpointHandlerMapping会覆盖掉spring-boot-actuator-autoconfigure jar中默认的bean

• 这个WebMvcEndpointHandlerMapping会覆盖掉spring-boot-actuator-autoconfigure jar中默认的bean，actuator endpoints就是在这里使用了PathPatternParser
• 上述两个步骤使spring和spring actuator不设置默认的pathPatternsCondition，而是使用ant_path_matcher
• 启动后访问http://localhost:8080/swagger-ui/index.html

方法二、将swagger切换成springdoc

• 参考https://springdoc.org/migrating-from-springfox.html

1、依赖

• pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.6.6version>
        <relativePath/> 
    parent>
    <groupId>com.examplegroupId>
    <artifactId>demoartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>demoname>
    <description>demodescription>
    <properties>
        <java.version>11java.version>
    properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        
        <dependency>
            <groupId>org.springdocgroupId>
            <artifactId>springdoc-openapi-uiartifactId>
            <version>1.6.8version>
        dependency>
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <optional>trueoptional>
        dependency>

    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombokgroupId>
                            <artifactId>lombokartifactId>
                        exclude>
                    excludes>
                configuration>
            plugin>
        plugins>
    build>

project>

2、在application.properties中设置

# 自定义文档访问的地址，http://localhost:8080/sss
springdoc.swagger-ui.path=/sss
# 需要扫描的包路径
springdoc.packagesToScan=com.example
# 匹配的url路径
springdoc.pathsToMatch=/*

3、配置类

package com.example.demo.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import io.swagger.v3.oas.models.ExternalDocumentation;
import io.swagger.v3.oas.models.OpenAPI;
import io.swagger.v3.oas.models.info.Info;
import io.swagger.v3.oas.models.info.License;

/**
 * @ClassName: SwaggerConfig
 * @Description:
 * @Author: Fisher
 * @Date: 2022/4/20 1:34 PM
 **/
@Configuration
public class SwaggerConfig {

    @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"));
    }
}

• 启动后访问http://localhost:8080/sss，最终会重定向到http://localhost:8080/swagger-ui/index.html