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我正在使用 Java EE、Glassfish 和 Netbeans 进行软件工程项目，但由于缺乏 Java 经验而遇到问题。

我正在开发一个网站，为用户提供创建一些活动的可能性。

我能够将event有关事件的信息（ID、名称、地点、日期、创建者）保存在一个表中，现在问题是填充另一个表calendar。在此表中只有 3 个属性：ID（自动和顺序生成）、创建者电子邮件和事件 ID。这个calendar表的目的是收集所有的用户事件：一个事件不仅可以耦合到它的创建者，还可以耦合到其他被邀请的用户。

当我尝试使表中的数据持久化时，calendar我得到了一个NullPointerException，因为在event表中 ID 是自动生成的，我认为当我调用该getEventID方法时，这个值仍然是null.

如何激活一个CalendarManager只需获取事件的创建者和ID并将它们写入calendar表中的事件？

我希望我很清楚，这里有一些文件：

EventManager工作正常：

@Stateless
public class EventManager {

    @PersistenceContext
    public EntityManager em;

    @Inject
    Principal principal;

    public void saveEvent(Event event) {
        em.persist(event);
    }

    public void deleteEvent(Event event) {
        em.remove(event);
    }

}

很好，CalendarEventsManager但没有收到正确的参数：

@Stateless
public class CalendarEventsManager {

    @PersistenceContext
    public EntityManager cm;

    @Inject
    Principal principal;

    public void saveCalendarEvents(CalendarEvents calendarevents) {
        cm.persist(calendarevents);     
    }

    public void deleteCalendarEvents(CalendarEvents calendarevents) {
        cm.remove(calendarevents);
    }
}

下面是用户单击“创建事件”时激活的 Bean 中的关键部分：

public String saveEvent() {
    /* obtain the creator's email */
    creator = um.getLoggedUser().getEmail();
    this.event.setCreator(creator);

    /* save information in db event */
    em.saveEvent(event);

    /* save information in db calendar */

    eventid = event.getID();
    this.calendarevents.setUserEmail(creator);
    this.calendarevents.setEventID(eventid);
    cm.saveCalendarEvents(calendarevents);

    /* next page to visualize */
    return "displayEvent";
}

直到em.saveEvent(event)一切正常并且数据库正确更新，但问题是当我这样做时eventid = getID()（getID在课堂上是公开的Event并且是正确的）。系统无法读取 ID，因为它没有从刚刚更新的数据库中读取。

这里有事件类：

@Entity
@Table(name="event")
public class Event implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private Integer id;
@NotNull(message = "May not be empty")
private String name;
@NotNull(message = "May not be empty")
private String place;
@NotNull(message = "May not be empty")
private String eventdate;
@NotNull(message = "May not be empty")
private String type;
@NotNull(message = "May not be empty")
private String visibility;
/*@NotNull(message = "May not be empty")
private String weather;*/
@NotNull(message = "May not be empty")
private String creator;

public void setID(Integer id){
    this.id = id;
}

public Integer getID() {
    return id;
}

public void setName(Integer id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getPlace() {
    return place;
}

public void setPlace(String place) {
    this.place = place;
}

public String getDate() {
    return eventdate;
}

public void setDate(String eventdate) {
    this.eventdate = eventdate;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
}

public String getVisibility() {
    return visibility;
}

public void setVisibility(String visibility) {
    this.visibility = visibility;
}

/*public String getWeather() {
    return weather;
}

public void setWeather(String weather) {
    this.weather = weather;
}*/

public String getCreator() {
    return creator;
}

public void setCreator(String creator) {
    this.creator = creator;
}

你有一些想法来解决这个问题吗？我已经阅读了@PostPersist注释，但我不知道如何正确应用它:(

感谢所有愿意帮助我的人的建议：D

EDIT1：错误可能在 saveEvent() 中的这段代码中：

    this.calendarevents.setUserEmail(creator);
    this.calendarevents.setEventId(eventid);
    System.out.println("event id after get is:   " + this.calendarevents.getUserEmail());
    System.out.println("event id after get is:   " + this.calendarevents.getEventId());
    cm.saveCalendarEvents(calendarevents);

我已将 system.out.println 用于验证该值，但错误出现在“this.calendarevents”中，因为没有 system.out 的迹象！这里有完整的 Bean！

@Named(value = "createBean")
@RequestScoped
public class CreateEventBean {

@EJB
private EventManager em;
@EJB
private UserManager um;

private Event event;
private String creator;

@EJB
private CalendarEventsManager cm;

private Integer eventid=0;
private CalendarEvents calendarevents;

public CreateEventBean() {
}

public Event getEvent() {
    if (event == null){
        event = new Event();
    }
    return event;
}

public void setEvent(Event event) {
    this.event = event;

}

public CalendarEvents getCalendarEvent() {
    if (calendarevents == null){
        calendarevents = new CalendarEvents();
    }
    return calendarevents;
}

public void setCalendarEvents(CalendarEvents calendarevents) {
    this.calendarevents = calendarevents;

}

public String saveEvent(){
    /*obtain the creator's email*/
    creator=um.getLoggedUser().getEmail();
    this.event.setCreator(creator);

    /*save information in db event*/
    em.saveEvent(event);

    /*save information in db calendar*/
    System.out.println("event id before get is:   " + eventid);
    eventid=event.getId();
    System.out.println("event id after get is:   " + eventid);

    this.calendarevents.setEventId(eventid);
    System.out.println("eventid in calendar could be:   " + this.calendarevents.getEventId());
    this.calendarevents.setUserEmail(creator);
    System.out.println("useremail in calendar could be:   " + this.calendarevents.getUserEmail());

    cm.saveCalendarEvents(calendarevents);



    /*next page to visualize*/
    return "displayEvent";
}

}

我真的没有发现“this.calendarevents.setEventId(eventid);”中的错误 那是第 80 行，错误是： 引起：警告：#{createBean.saveEvent()}：java.lang.NullPointerException javax.faces.FacesException：#{createBean.saveEvent()}：java.lang.NullPointerException [引起：java.lang.NullPointerException at it.nyquistmeteocal.beans.CreateEventBean.saveEvent(CreateEventBean.java:80)]

这是 CalendarEvents 类：

@Entity
@Table(name="calendarevents")
public class CalendarEvents implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private Integer id;
@NotNull(message = "May not be empty")
private String useremail;
@NotNull(message = "May not be empty")
private Integer eventid;


public Integer getId() {
    return id;
}

public void setName(Integer id) {
    this.id = id;
}

public String getUserEmail() {
    return useremail;
}

public void setUserEmail(String useremail) {
    this.useremail = useremail;
}


public Integer getEventId() {
    return eventid;
}

public void setEventId(Integer eventid) {
    this.eventid = eventid;
}


}
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1 回答 1

0

我已经解决了问题！！

我只是以这种方式修改了 calendarevents 的声明：

private CalendarEvents calendarevents = new CalendarEvents();

在我认为如果 calendarevents 指向 NULL 它将执行这部分代码之前，我没有这样做：

public CalendarEvents getCalendarEvent() {
    if (this.calendarevents == null){
        this.calendarevents = new CalendarEvents();
    }
    return this.calendarevents;
}

public void setCalendarEvents(CalendarEvents calendarevents) {
    calendarevents = calendarevents;

}

这是否意味着我不需要最后一部分？:)

于 2014-12-15T19:46:26.893 回答