Question

我在会话范围内有两个托管bean。第一个是简单的元素列表。

@ManagedBean (name = TrainList.BEAN_NAME)
@SessionScoped
public class TrainList extends ListBasic<TrainObj> {    

    private static final long serialVersionUID = 1L;
    public static final String BEAN_NAME = "trainList";

    public TrainList ()  {
        super();
    }
}

其次表示列表中特定记录的详细信息，并在用户单击第一个列表中的记录后调用。

@ManagedBean (name = TrainForm.BEAN_NAME)
@SessionScoped
public class TrainForm extends TrainObj {
    private static final Logger logger = Logger.getLogger(TrainForm.class.getName());
    public static final String BEAN_NAME = "trainForm";

    @ManagedProperty(value = "#{trainList}")
    private TrainList trainList; /* + getter and setter */


    public TrainForm ()  {
        super();
    }

    public void refreshList(){
     if (trainList != null) {
            logger.debug(" trainlist is not null");
             trainList.refreshList();
        }
        else {
            logger.debug(" trainlist is NULL");
        }
}

所以list bean在第二个之前初始化。但是从第二个访问第一个bean时仍然是null？

[2014-11-12 13:18] DEBUG [http-apr-8080-exec-7] - com.kropla.TrainForm.update(TrainForm.java:xx) - trainlist is NULL

有什么问题？

[请不要投票 - 我已经搜索了答案，但没有找到合适/合适的答案]

我可以列出所有托管bean（https://stackoverflow.com/a/15503044/2303190），这个bean在列表中。但为什么我会变为空？

Answer 1

尝试像这样获取bean。我在我的应用程序中使用了以下代码，但是使用@ViewScoped你的是SessionScoped，尝试这可能有用。

FacesContext context = FacesContext.getCurrentInstance();
TrainList trainList = context.getApplication().evaluateExpressionGet(context, "#{trainList}",TrainList.class);

Answer 2

似乎问题与第一个初始化（调用）第二个bean的方式有关。

private String returnDetailPageName(TrainObj entityObj) {
        Map session = FacesContext.getCurrentInstance().getExternalContext().getSessionMap();
        TrainForm formBean = new TrainForm();
        formBean.setMe(entityObj); //setter for the entity vproperties
        session.put(formBeanName , formBean);
        return "goProdTraining"; //go to detail page
    }

此＆＃34;会话＆＃34;调用bean的方法是创建一个没有存储在JSF中的新bean。通过ManagedProperty更改调用bean属性，使用PostConstruct将父bean分配给子bean（以防止循环循环）：

@ManagedBean (name = TrainList.BEAN_NAME)
@SessionScoped
public class TrainList extends ListBasic<TrainObj> {    

    private static final long serialVersionUID = 1L;
    public static final String BEAN_NAME = "trainList";

    public TrainList ()  { super();}

    @ManagedProperty (value = "#{trainForm}")
    private TrainForm trainForm; //with getter&setter

    @PostConstruct
    private void setChildBeanProperty(){
        this.trainForm.setTrainList(this);
    }
}


@ManagedBean (name = TrainForm.BEAN_NAME)
@SessionScoped
public class TrainForm extends TrainObj {
    private static final Logger logger = Logger.getLogger(TrainForm.class.getName());
    public static final String BEAN_NAME = "trainForm";

    private TrainList trainList; /* + getter and setter */

    public TrainForm ()  {
        super();
    }

    public void refreshList(){
     if (trainList != null) {
            logger.debug(" trainlist is not null");
             trainList.refreshList();
        }
        else {
            logger.debug(" trainlist is NULL");
        }
}

通过@ManagedBean调用托管bean时为空

2 个答案: