“Failed to start bean ‘documentationPluginsBootstrapper”高版本Springboot（2.6+）加入Swagger报错问题

“org.springframework.context.ApplicationContextException: Failed to start bean ‘documentationPluginsBootstrapper’; nested exception is java.lang.NullPointerException ”

Bug输出 

问题原因：是由于用了高版本Springboot原因（2.7.5），降到2.6一下就是正常的。

因为Springfox 使用的路径匹配是基于AntPathMatcher的，而Spring Boot 2.6.X使用的是PathPatternMatcher。

如何解决呢，以下方案：

1.application.yml 或applicaiton.properties 中添加如下配置

spring:
  mvc:
    pathmatch:
      matching-strategy: ant_path_matcher

2.加入依赖（加入knife4j UI）

        <!--swagger 高版本Springboot2.6+使用3.0以上-->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>3.0.0</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>
        <!--swagger ui 高版本Springboot2.6+使用3.0以上-->
        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>knife4j-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>

3.编写配置文件：SwaggerConfig

package com.cn.config.swagger;

import io.swagger.annotations.ApiOperation;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.util.ReflectionUtils;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.RequestMappingInfoHandlerMapping;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.ParameterBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.schema.ModelRef;
import springfox.documentation.service.*;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spi.service.contexts.SecurityContext;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.spring.web.plugins.WebFluxRequestHandlerProvider;
import springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @program: toolbox-common
 * @description
 * @date 2023/3/9
 */
@Configuration
public class SwaggerConfig {

    /**
     * swagger2的配置文件，这里可以配置swagger2的一些基本的内容，比如扫描的包等等
     *
     * @return Docket
     */
    @Bean(value = "defaultApi2")
    public Docket defaultApi2() {
        return new Docket(DocumentationType.SWAGGER_2)
                //是否启用Swagger
                .enable(true)
                .apiInfo(apiInfo())
                .select()
                //此包路径下的类，才生成接口文档
                //.apis(RequestHandlerSelectors.basePackage("com.cn"))
                //扫描所有
                //.apis(RequestHandlerSelectors.any())
                //加了ApiOperation注解的类，才生成接口文档
                .apis(RequestHandlerSelectors.withClassAnnotation(RestController.class))
                .apis(RequestHandlerSelectors.withMethodAnnotation(ApiOperation.class))
                .paths(PathSelectors.any())
                .build()
                //设置自定义swagger请求头
                .securitySchemes(Collections.singletonList(securityScheme()))
                .securityContexts(securityContexts());
                //.globalOperationParameters(setHeaderToken());
    }
    /**
     * 设置自定义swagger请求头
     * @return ApiKey
     */
    @Bean
    SecurityScheme securityScheme() {
        return new ApiKey("Access-Token", "Access-Token", "header");
    }

    /**
     * 新增 securityContexts 保持登录状态
     */
    private List<SecurityContext> securityContexts() {
        return new ArrayList(
                Collections.singleton(SecurityContext.builder()
                        .securityReferences(defaultAuth())
                        .forPaths(PathSelectors.regex("^(?!auth).*$"))
                        .build())
        );
    }

    /**
     * 配置
     */
    private List<SecurityReference> defaultAuth() {
        AuthorizationScope authorizationScope = new AuthorizationScope("global", "accessEverything");
        AuthorizationScope[] authorizationScopes = new AuthorizationScope[1];
        authorizationScopes[0] = authorizationScope;
        return new ArrayList(
                Collections.singleton(new SecurityReference("Access-Token", authorizationScopes)));
    }

    /**
     * swagger主页名
     * @return ApiInfo
     */
    private ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("接口文档")
                .description("swagger接口文档")
                .version("1.0")
                .build();
    }

    /**
     * JWT token
     * @return setHeaderToken
     */
    private List<Parameter> setHeaderToken() {
        ParameterBuilder tokenPar = new ParameterBuilder();
        List<Parameter> pars = new ArrayList<>();
        tokenPar.name("Access-Token").description("token").modelRef(new ModelRef("string")).parameterType("header").required(false).build();
        pars.add(tokenPar.build());
        return pars;
    }
    
    /**
     * 务必加入配置类中的springfoxHandlerProviderBeanPostProcessor方法
     * @return BeanPostProcessor
     */
    @Bean
    public static BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
        return new BeanPostProcessor() {

            @Override
            public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
                if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
                    customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
                }
                return bean;
            }

            private <T extends RequestMappingInfoHandlerMapping> void customizeSpringfoxHandlerMappings(List<T> mappings) {
                List<T> copy = mappings.stream()
                        .filter(mapping -> mapping.getPatternParser() == null)
                        .collect(Collectors.toList());
                mappings.clear();
                mappings.addAll(copy);
            }

            @SuppressWarnings("unchecked")
            private List<RequestMappingInfoHandlerMapping> getHandlerMappings(Object bean) {
                try {
                    Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
                    field.setAccessible(true);
                    return (List<RequestMappingInfoHandlerMapping>) field.get(bean);
                } catch (IllegalArgumentException | IllegalAccessException e) {
                    throw new IllegalStateException(e);
                }
            }
        };
    }

}

4.1.swagger ui 页面

4.2.knife4j UI 页面

 5.总结

• ​务必加入配置类中的springfoxHandlerProviderBeanPostProcessor方法。
• yaml文件中必须将匹配策略改为ant_path_matcher。
• 配置类中必须有springfoxHandlerProviderBeanPostProcessor方法。