Spring Boot 2.6集成knife4j，解决Failed to start bean ‘documentationPluginsBootstrapper‘

本次学习参考 官方文档
本次示例采用Spring Boot 2.6.3
完整的pom.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<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>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.alex</groupId>
    <artifactId>knife4j-spring-boot-fast-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>knife4j-spring-boot-fast-demo</name>
    <description>knife4j-spring-boot-fast-demo</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>knife4j-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

先引入Knife4j包

参考pom.xml文件，引入knife4j-spring-boot-starter。

创建Swagger配置依赖

代码如下：

package com.alex.knife4jspringbootfastdemo.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2WebMvc;

@Configuration
@EnableSwagger2WebMvc
public class Knife4jConfiguration {

    @Bean(value = "defaultApi2")
    public Docket defaultApi2(){
        Docket docket=new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(new ApiInfoBuilder()
                        .title("测试api文档")
                        .description("描述")
                        .termsOfServiceUrl("http://www.baidu.com")
//                        .contact("abc@qq.com")
                        .version("1.0")
                        .build())
                .groupName("2.X版本")
                .select()
                .apis(RequestHandlerSelectors.basePackage("com.alex.knife4jspringbootfastdemo.controller"))
                .paths(PathSelectors.any())
                .build();
        return docket;
    }
}

创建实例Controller

代码如下：

package com.alex.knife4jspringbootfastdemo.controller;

import io.swagger.annotations.Api;
import io.swagger.annotations.ApiImplicitParam;
import io.swagger.annotations.ApiOperation;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@Api(tags = "首页模块")
@RestController
public class IndexController {

    @ApiImplicitParam(name = "name",value = "姓名",required = true)
    @ApiOperation(value = "向客人问好")
    @GetMapping("/sayHi")
    public ResponseEntity<String> sayHi(@RequestParam(value = "name") String name){
        return ResponseEntity.ok("Hi:"+name);
    }
}

解决问题

问题:

> Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException: Cannot invoke "org.springframework.web.servlet.mvc.condition.PatternsRequestCondition.toString()" because the return value of "springfox.documentation.spi.service.contexts.Orderings.patternsCondition(springfox.documentation.RequestHandler)" is null

原因

Springboot2.6以后将SpringMVC 默认路径匹配策略从AntPathMatcher 更改为PathPatternParser，导致出错

解决办法

网上的方法是降低SpringBoot版本，感觉不太合适，其实解决很简单
在配置文件application.properties中加入

spring.mvc.pathmatch.matching-strategy=ANT_PATH_MATCHER

效果