Spring中 如果该Service有多个实现类，它怎么知道该注入哪个ServiceImpl类？

接口

public interface HumanService {
    public String name();
}

接口实现类 

@Service("teacherService")
public class TeacherServiceImpl implements HumanService {
    @Override
    public String name() {
        System.out.println("teacher");
        return "teacher";
    }
}

@Service("doctorService")
public class DoctorServiceImpl implements HumanService {
    @Override
    public String name() {
        System.out.println("doctor");
        return "doctor";
    }
}

控制器 

@RestController
public class HumanController {
//    @Resource(name="doctorService")

    @Autowired
    @Qualifier("teacherService")
    private HumanService humanService;

    @RequestMapping("/name")
    public String name(){
        return humanService.name();
    }
}