java工具类中注入service，dao类

@Component
public class ExcelUtils {
    @Resource
    private SysUserMapper sysUserMapper; 

    private static ExcelUtils exceltUtils;

    @PostConstruct
    public void init() {
        excelUtils = this;
        excelUtils.sysUsreMapper = this.sysUserMapper;
    }

    public void exportExcel(...) {
        SysUserVO vo = excelUtils.sysUserMapper.selectByPrimaryKey(id);
        //...
    }
}