我不能使用@ManagedProperty访问会话范围变量吗？

Question

I know I can put/get session scope variables like this.

FacesContext.getCurrentInstance().getExternalContext()
    .getSessionMap().put(SESSION_KEY_SOME, some);

Then can't I access the value like this?

@ManagedBean
@SessionScoped
public class SomeOtherBean {

    @ManagedProperty("#{sessionScope.some}")
    private Some some;
}

The value is null .

Answer 1

@ManagedProperty runs during creation/instantiation of the @ManagedBean .

So, when the @ManagedBean is created before the #{sessionScope.some} is set for first time, then it will still remain null in the @ManagedBean . It will only work when @ManagedBean is created after the #{sessionScope.some} is set for the first time.

There are basically three ways to achieve the desired behavior.

1. Replace private Some some by externalContext.getSessionMap().get("some") .

    @ManagedBean @SessionScoped public class SomeOtherBean { public void someMethod() { Some some = (Some) FacesContext.getCurrentInstance() .getExternalContext().getSessionMap().get("some"); // ... } } 

2. Replace @SessionScoped by @RequestScoped .

    @ManagedBean @RequestScoped public class SomeOtherBean { @ManagedProperty("#{sessionScope.some}") private Some some; // ... } 

3. Replace externalContext.getSessionMap().put("some", some) by directly setting it as bean property.

    @ManagedBean public class SomeBean { @ManagedProperty("#{someOtherBean}") private SomeOtherBean someOtherBean; public void someMethod() { // ... someOtherBean.setSome(some); } // ... } 

See also:

• How to choose the right bean scope?