what is none scope bean and when to use it?

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A bean with a <managed-bean-scope> of none or a @NoneScoped annotation will be created on every single EL expression referencing the bean. It isn’t been stored by JSF anywhere. The caller has got to store the evaluated reference itself, if necessary.

E.g. the following in the view

<p>#{noneScopedBean.someProperty}</p>
<p>#{noneScopedBean.someProperty}</p>
<p>#{noneScopedBean.someProperty}</p>

on a none-scoped bean will construct the bean 3 (three) times during a request. Every access to the bean gives a completely separate bean which is been garbaged immediately after the property access.

However, the following in for example a session scoped bean

@ManagedProperty("#{noneScopedBean}")
private NoneScopedBean noneScopedBean;

will make it to live as long as the session scoped bean instance. You should only make sure that you access it in the view by #{sessionScopedBean.noneScopedBean.someProperty} instead.

So it may be useful when you want scope-less data being available as a managed property in an arbitrary bean.

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