1、数据库中表的结构如下

2、excel中的数据如下

3、定义一个与excel表中对应的实体类

@Data
public class SubjectData {

    @ExcelProperty(index = 0)
    private String oneSubjectName;

    @ExcelProperty(index = 1)
    private String twoSubjectName;
}

4、controller

@RestController
public class EduSubjectController {

    @Autowired
    EduSubjectService eduSubjectService;

//  获取上传的Excel文件，从文件中读取数据保存到数据库中
    @PostMapping("addSubject")
    public R addSubject(MultipartFile file){
        eduSubjectService.addSubject(file,eduSubjectService);
        return R.ok();
    }

}

5、service

@Service
public class EduSubjectServiceImpl extends ServiceImpl<EduSubjectMapper, EduSubject> implements EduSubjectService {

    @Override
    public void addSubject(MultipartFile file, EduSubjectService eduSubjectService) {
        //文件输入流
        InputStream in = null;
        try {
            in = file.getInputStream();
            //调用方法进行读取,通过带参数的构造器将spring容器中的EduSubjectService对象传入到监听器中
            EasyExcel.read(in, SubjectData.class,new SubjectExcelListener(eduSubjectService)).sheet().doRead();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

6、编写excel的listener

public class SubjectExcelListener extends AnalysisEventListener<SubjectData> {

    //因为SubjectExcelListener不能交给spring进行管理，需要自己new，不能注入其他对象
    //不能实现数据库操作
    private EduSubjectService eduSubjectService;
    public SubjectExcelListener() {
    }

    public SubjectExcelListener(EduSubjectService eduSubjectService) {
        this.eduSubjectService = eduSubjectService;
    }

    //读取excel内容，一行一行进行读取，不会读取excel中的表头数据
    @Override
    public void invoke(SubjectData subjectData, AnalysisContext analysisContext) {
        if(subjectData==null){
            throw new MyException(20001,"文件中的数据为空！");
        }
        //一行一行读取，每次读取有两个值，第一个值一级分类，第二个值二级分类
        //判断一级分类是否重复
//        判断数据库中是否存在一级分类，如果不存在则添加到数据库
        EduSubject eduSubject = existOneSubject(eduSubjectService, subjectData.getOneSubjectName());
        if(eduSubject==null){
            eduSubject=new EduSubject();
            eduSubject.setParentId("0");
            eduSubject.setTitle(subjectData.getOneSubjectName());
            eduSubjectService.save(eduSubject);
        }
//        如果一级分类在数据库中存在则获取一级分类的id作为二级分类的parent_id
        String pid=eduSubject.getId();
        EduSubject eduSubjectTwo = existTwoSubject(eduSubjectService, subjectData.getTwoSubjectName(), pid);
        if(eduSubjectTwo==null){
            eduSubjectTwo=new EduSubject();
            eduSubjectTwo.setParentId(pid);
            eduSubjectTwo.setTitle(subjectData.getTwoSubjectName());
            eduSubjectService.save(eduSubjectTwo);
        }

    }

     //判断一级分类不能重复添加
    public EduSubject existOneSubject(EduSubjectService eduSubjectService,String subjectName){
        QueryWrapper<EduSubject> eduSubjectQueryWrapper = new QueryWrapper<>();
        eduSubjectQueryWrapper.eq("title",subjectName);
        eduSubjectQueryWrapper.eq("parent_id","0");
        EduSubject one = eduSubjectService.getOne(eduSubjectQueryWrapper);
        return one;
    }

    //判断二级分类不能重复添加
    public EduSubject existTwoSubject(EduSubjectService eduSubjectService,String subjectName,String pid){
        QueryWrapper<EduSubject> eduSubjectQueryWrapper = new QueryWrapper<>();
        eduSubjectQueryWrapper.eq("title",subjectName);
        eduSubjectQueryWrapper.eq("parent_id",pid);
        EduSubject two = eduSubjectService.getOne(eduSubjectQueryWrapper);
        return two;
    }

    @Override
    public void doAfterAllAnalysed(AnalysisContext analysisContext) {

    }
}