java工具类中注入service，dao类

@Componentpublic 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);        //...    }}