问Spring Boot项目出现依赖注入异常应该怎么解决？

@Mapper
public interface AdminMapper {

    @Select("select user_count from t_usercount")
    Integer getUserCount();
    
}

@Service
@Transactional(propagation=Propagation.REQUIRED, isolation=Isolation.DEFAULT)
public class AdminServiceImpl implements AdminService {

    @Autowired
    private AdminMapper am;

    @Override
    @Transactional(readOnly=true)
    public BackJSON getUserCount() {
        BackJSON json = new BackJSON(200);
        String count = "{\"count\":"+am.getUserCount()+"}";
        json.setData(JSONObject.parse(count));
        return json;
    }

}