解决springBoot整合knife4j报错的问题

依赖：

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

knife4j配置文件：

package com.example.family.Configuration;


import com.github.xiaoymin.knife4j.spring.extension.OpenApiExtensionResolver;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
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.service.ApiInfo;
import springfox.documentation.service.Contact;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2;

@Configuration
@EnableSwagger2//Swagger3版本使用这个注解
public class Knife4jConfiguration {


    /*引入Knife4j提供的扩展类*/
    private final OpenApiExtensionResolver openApiExtensionResolver;

    @Autowired
    public Knife4jConfiguration(OpenApiExtensionResolver openApiExtensionResolver) {
        this.openApiExtensionResolver = openApiExtensionResolver;
    }

    @Bean(value = "defaultApi2")
    public Docket userApi() {
        String groupName =  "用户管理API";
        return new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(apiInfo())
                .groupName(groupName)
                .select()
                //在设置的包下的会生效
              .apis(RequestHandlerSelectors.basePackage("com.example.family.Controller.UserController"))
                //只有标注了ApiOperation的方法才会生效
//                .apis(RequestHandlerSelectors.withMethodAnnotation(ApiOperation.class))
                .paths(PathSelectors.any())
                .build()
                //赋予插件体系
                .extensions(openApiExtensionResolver.buildExtensions(groupName));

    }

    @Bean(value = "defaultApi3")
    public Docket testApi() {
        String groupName =  "测试API";
        return new Docket(DocumentationType.SWAGGER_2)
                .apiInfo(apiInfo())
                .groupName(groupName)
                .select()
                //在设置的包下的会生效
                .apis(RequestHandlerSelectors.basePackage("com.example.family.Controller.Test"))
                //只有标注了ApiOperation的方法才会生效
//                .apis(RequestHandlerSelectors.withMethodAnnotation(ApiOperation.class))
                .paths(PathSelectors.any())
                .build()
                //赋予插件体系
                .extensions(openApiExtensionResolver.buildExtensions(groupName));

    }

    private ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("family后台服务API")
                .description("整合knife4j搭建的后台服务API接口文档")
                .contact(new Contact("减肥", null, "[email protected]"))
                .termsOfServiceUrl("http://localhost:8080/")
                .version("1.0.0")
                .build();
    }
}

controller层：

package com.example.family.Controller.UserController;

import cn.hutool.core.bean.BeanUtil;
import cn.hutool.core.bean.copier.CopyOptions;
import com.example.family.DAO.UserDAO;
import com.example.family.DTO.UserQueryDTo;
import com.example.family.Pojo.User;
import com.example.family.ResponseDTO.Result;
import com.example.family.ResponseDTO.ResultEntry;
import com.example.family.ResponseDTO.ResultEnum;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Example;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@Api(tags = "用户管理")
@RequestMapping("user")
public class UserController {

    @Autowired
    UserDAO userDAO;

    @ApiOperation("查询用户")
    @GetMapping("search")
    public Result<List<User>> test1(UserQueryDTo dto){
        User user = new User();
        BeanUtil.copyProperties(dto,user, CopyOptions.create().setIgnoreNullValue(true).setIgnoreError(true));
        Example<User> example = Example.of(user);
        return ResultEntry.error(userDAO.findAll(example), ResultEnum.RESULT_NOT_EXIST);
    }

}

报错信息：Unable to scan documentation context default  java.lang.NullPointerException: null

出错原因：将类中的属性设置为了public类型

解决办法：将public删除或者改为private就可以啦