ManagedProperty in CDI @Named bean returns null

问题

I\'m trying to deal with @ManagedProperty but without success !

I\'ve been following this guide, and it not seems that hard. But my code simply won\'t work!

Here\'s a little snippet

@ManagedBean
@SessionScoped
public class LoginBean {

@EJB
private LoginUserLocal loginUser;
private boolean loggedIn = false;
private User user;
private StreamedContent image;
.
.
.
//--
@Named(value = \"messagesBean\")
@RequestScoped
public class MessagesBean {

@ManagedProperty(value = \"#{loginBean}\")
private LoginBean loginBean;

public LoginBean getLoginBean() {
    return loginBean;
}

public void setLoginBean(LoginBean loginBean) {
    this.loginBean = loginBean;
}

public String getUser() {
    System.err.println(loginBean == null);
    return loginBean.getUser().getUsername();
}

This code gives me a NullPointerException, saying that loginBean is null!

Any suggestion?

回答1:

You are mixing JSF managed beans with CDI beans. Your LoginBean is a JSF managed bean (it has the @ManagedBean annotation). Your MessageBean is a CDI bean (it has the @Named annotation). If you changed the Message bean to a JSF managed bean (replacing @Named with @ManagedBean) then the problem should be solved (It should work with two CDI beans as well).

Here is a short overview of how injection works between both bean types:

CDI @Named --> CDI @Named (works)

CDI @Named --> JSF @ManagedBean (works only if scope of injected bean is broader)

JSF @ManagedBean --> JSF @ManagedBean (works only if scope of injected bean is broader)

JSF @ManagedBean --> CDI @Named (won't work)

But take care of the scope import classes. There are different classes for @SessionScoped and @RequestScoped depending on the bean type.

javax.faces.bean.SessionScoped for @ManagedBeans

javax.enterprise.context.SessionScoped for CDI @Named beans

In addition, for @Named (CDI) use @Inject and for @ManagedBean use @ManagedProperty. There is one thing that does not work in CDI. Your @ManagedProperty(value = "#{loginBean}") gets a full bean, but @ManagedProperty(value = "#{loginBean.user}") to get a 'property' of a bean works to. This is not directly possible in CDI with @Inject. See CDI Replacement for @ManagedProperty for a 'solution'

来源：https://stackoverflow.com/questions/9921324/managedproperty-in-cdi-named-bean-returns-null