服务层EJB空指针异常

Question

我有一个postConstruct方法：

@EJB
private VisitServiceLocal visitService;

@PostConstruct
void init() {
    eventModel = new DefaultScheduleModel();
    visits = getDoctorVisits();
}

方法：

public List<Visit> getDoctorVisits() {
    doctorId = (Integer) session.getAttribute("userId");
    return visitService.findMyVisits(doctorId);
}

VisitService：

@Override
public List<Visit> findMyVisits(Integer myId) {
    return visitDao.findMyVisits(myId);
}

@Override
public List<Visit> findMyVisits(Integer myId) {
    currentDate = new Date();
    try {
        Query q = em.createQuery("SELECT v FROM Visit v WHERE v.doctorId.id = :myId and v.visitStart > :currentDate");
        q.setParameter("myId", myId);
        q.setParameter("currentDate", currentDate);
        List<Visit> visits = q.getResultList();
        return visits;
    } catch (Exception e) {
        System.out.println("Błąd: " + e.getMessage());
        return null;
    }
}

方法：

public List<Visit> getDoctorVisits() {
    doctorId = (Integer) session.getAttribute("userId");
    return visitDao.findMyVisits(doctorId);
}

为什么添加服务层会产生此错误？在服务层，我只导致dao方法。

Answer 1

Caused by: java.lang.NullPointerException
    at pl.ePrzychodnia.dao.serviceClass.VisitService.findMyVisits(VisitService.java:89) at 

你曲解了问题。问题不在JSF方面。问题出在EJB端。visitservice已正确注入，但在visitservice本身内，visitdao未正确注入。

您没有显示所有代码，但很可能有一个

@Stateless
public class VisitService implements VisitServiceLocal {

    private VisitDao visitDao;

    @Override
    public List<Visit> findMyVisits(Integer myId) {
        return visitDao.findMyVisits(myId);
    }

}

在这种情况下，您也需要在那里注入它：

@Stateless
public class VisitService implements VisitServiceLocal {

    @EJB
    private VisitDao visitDao;

    @Override
    public List<Visit> findMyVisits(Integer myId) {
        return visitDao.findMyVisits(myId);
    }

}