@ManagedProperty不反映更改，并始终返回null [英] @ManagedProperty does not reflect changes and keeps returning null

问题描述

我试图将一个sessionscoped bean的值注入到viewscoped bean中，但是它一直返回null，这是一个代码段:

I'm trying to inject the value of one sessionscoped bean into a viewscoped bean but it keeps returning null, here's a snippet:

import javax.faces.application.FacesMessage;
import javax.faces.bean.SessionScoped;
import javax.faces.bean.ManagedBean;
import javax.faces.context.FacesContext;

//Class for managing the current logged-in user
@ManagedBean(name="user")
@SessionScoped
public class User implements Serializable{

private String userName;

public void setUserName(String userName) {
    this.userName = userName;
}
public String getUserName() {
    return this.userName;
}

它用在:

@ManagedBean(name="databrowser")
@ViewScoped
public class dataBrowser implements Serializable {  

private List<UploadData> dataItems;
private SelectItem[] dataTypeOptions, qualityOptions, accessOptions;
private UploadData selectedData;
private String filelocation;

@ManagedProperty(value="#{user.userName}")
private String userName;

public String getUserName() {
    return this.userName;
}

dataBrowser用于填充Primefaces数据表，当它被称为userName为null且我不确定为什么时.

dataBrowser is used to populate a Primefaces datatable, when it's called userName is null and I'm not sure why.

推荐答案

最近，我也对通过@ManagedProperties注入嵌套的托管Bean属性存在问题.一旦注入，它就永远不会改变.我通过在吸气剂中评估EL而不是注入EL来进行变通.

Recently I have problem with injecting nested managed bean properties by @ManagedProperties too. Once injected it never changed. I did a workaround by evaluating EL in getter instead of injecting it.

尝试:

public String getUserName() {
    FacesContext context = FacesContext.getCurrentInstance();
    return (String) context.getApplication().evaluateExpressionGet(context,"#{user.userName}", String.class);
}

您还可以尝试注入整个user bean，并在getter中从中获取userName字段.

You can also try injecting entire user bean and get userName field from it in getter.

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