导出模板代码，原理是combo属性 传递一个数组 里面是label下拉数组。

    @Override
    public void downloadTemplate(HttpServletResponse response) {
        ExcelUtil<ThMachineryManageExcel> util = new ExcelUtil<>(ThMachineryManageExcel.class);
        List<SysDistrictExcel> districtExcelCache = DistrictUtils.getDistrictExcelCache();
        String[] array = districtExcelCache.stream()
                .map(SysDistrictExcel::getName)
                .toArray(String[]::new);
        util.combo("districtCode", array);
        util.importTemplateExcel(response, "数据模板");
    }

导入代码映射逻辑 util.readConverterExp 映射数据，数据结构是String类型多个逗号隔开：label=value

  @Override
    public R<?> importData(MultipartFile file) throws IOException {
        ExcelUtil<ThMachineryManageExcel> util = new ExcelUtil<>(ThMachineryManageExcel.class);
        List<SysDistrictExcel> districtExcelCache = DistrictUtils.getDistrictExcelCache();
        Map<String, SysDistrictExcel> districtMap = districtExcelCache.stream()
                .collect(Collectors.toMap(SysDistrictExcel::getCode, district -> district));
        String readConverterExp = districtExcelCache.stream()
                .map(district -> district.getCode() + "=" + district.getName())
                .collect(Collectors.joining(","));
        // 映射数据label和value        
        util.readConverterExp("districtCode", readConverterExp);
        List<ThMachineryManageExcel> excelList = util.importExcel(file.getInputStream());
        if (ObjectUtil.isEmpty(excelList)){
            throw new ServiceException("导入数据不能为空！");
        }
        List<ThMachineryManage> saveOrUpdateList = new ArrayList<>();

        int successNum = 0;
        int updateNum = 0;
        int errorNum = 0;
        StringBuilder successMsg = new StringBuilder();
        for (ThMachineryManageExcel data : excelList){
            try {
                ThMachineryManage topic = BeanUtil.copyProperties(data, ThMachineryManage.class);
                //校验基本数据
                BeanValidators.validateWithException(validator,topic);
                ThMachineryManage oneData = getOne(new LambdaQueryWrapper<ThMachineryManage>().eq(ThMachineryManage::getBrand, data.getBrand()));
                //校验通过 开始检测数据是否重复
                if (ObjectUtil.isNotNull(oneData)){
                    //说明是更新数据
                    topic.setId(oneData.getId());
                    updateNum++;
                }else {
                    successNum++;
                }
                SysDistrictExcel sysDistrictExcel = districtMap.get(data.getDistrictCode());
                //业务逻辑  存储行政区更多的数据
                topic.setCountyCode(sysDistrictExcel.getCountyCode());
                topic.setTownCode(sysDistrictExcel.getTownCode());
                topic.setVillageCode(sysDistrictExcel.getVillageCode());
                topic.setDistrictLevel("2");
                topic.setDistrictName(sysDistrictExcel.getName());
                saveOrUpdateList.add(topic);
            }catch (Exception e){
                errorNum++;
                int count = excelList.indexOf(data);
                String message = e.getMessage();
                successMsg.append("第").append(count+1).append("条数据导入失败，原因：").append(message).append(";");
                break;
            }
        }
        // 数据全部正确时 进行批量插入/更新
        if (!saveOrUpdateList.isEmpty()&&errorNum==0){
            super.saveOrUpdateBatch(saveOrUpdateList);
            if (successNum>0){
                successMsg.append("成功导入").append(successNum).append("条数据");
            }
            if (updateNum>0){
                successMsg.append("成功更新").append(updateNum).append("条数据");
            }
            return R.ok(successMsg.toString());
        }else {
            return R.fail(successMsg.toString());
        }
    }