ViewScoped (OmniFaces 2.5 API)

```
@Inherited
 @Documented
 @NormalScope(passivating=true)
 @Retention(value=RUNTIME)
 @Target(value={TYPE,METHOD,FIELD})
public @interface ViewScoped
```
The CDI view scope annotation, with more optimal handling of bean destroy as compared to standard JSF one.
In standard JSF 2.0/2.1, the @PreDestroy annotated method on a view scoped bean was never invoked when the session expires. Since OmniFaces 1.6, this CDI view scope annotation will guarantee that the @PreDestroy annotated method is also invoked on session expire. Since JSF 2.2, this problem is solved on native JSF view scoped beans, hereby making this annotation superflous in JSF 2.2.
However, there may be cases when it's desirable to immediately destroy a view scoped bean as well when the browser unload event is invoked. I.e. when the user navigates away by GET, or closes the browser tab/window. None of the both JSF 2.2 view scope annotations support this. Since OmniFaces 2.2, this CDI view scope annotation will guarantee that the @PreDestroy annotated method is also invoked on browser unload. This trick is done by a synchronous XHR request via an automatically included helper script omnifaces:unload.js. There's however a small caveat: on slow network and/or poor server hardware, there may be a noticeable lag between the enduser action of unloading the page and the desired result. If this is undesireable, then better stick to JSF 2.2's own view scope annotations and accept the postponed destroy.
Since OmniFaces 2.3, the unload has been further improved to also physically remove the associated JSF view state from JSF implementation's internal LRU map in case of server side state saving, hereby further decreasing the risk at ViewExpiredException on the other views which were created/opened earlier. As side effect of this change, the @PreDestroy annotated method of any standard JSF view scoped beans referenced in the same view as the OmniFaces CDI view scoped bean will also guaranteed be invoked on browser unload.
In a nutshell: if you're on JSF 2.0/2.1, and you can't upgrade to JSF 2.2, and you want the @PreDestroy to be invoked on sesison expire too, then use OmniFaces 1.6+ with this view scope annotation. Or, if you're on JSF 2.2 already, and you want the @PreDestroy to be invoked on browser unload too, then use OmniFaces 2.2+ with this view scope annotation.
Related JSF issues:
Usage

Just use it the usual way as all other CDI scopes. Watch out with IDE autocomplete on import that you don't accidentally import standard JSF's own one.
```
 import javax.inject.Named;
 import org.omnifaces.cdi.ViewScoped;

 @Named
 @ViewScoped
 public class OmniCDIViewScopedBean implements Serializable {}
 
```
Please note that the bean must implement Serializable, otherwise the CDI implementation will throw an exception about the bean not being passivation capable.
Under the covers, CDI managed beans with this scope are via ViewScopeManager stored in the session scope by an UUID based key which is referenced in JSF's own view map as available by UIViewRoot.getViewMap(). They are not stored in the JSF view map itself as that would be rather expensive in case of client side state saving.
Configuration

By default, the maximum number of active view scopes is hold in a LRU map with a default size equal to the first non-null value of the following context parameters:
- "org.omnifaces.VIEW_SCOPE_MANAGER_MAX_ACTIVE_VIEW_SCOPES" (OmniFaces)
- "com.sun.faces.numberOfLogicalViews" (Mojarra-specific)
- "org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION" (MyFaces-specific)
If none of those context parameters are present, then a default size of 20 will be used. When a view scoped bean is evicted from the LRU map, then its @PreDestroy will also guaranteed to be invoked.
Since:

1.6

Author:

Radu Creanga <rdcrng@gmail.com>, Bauke Scholtz

See Also:

ViewScopeExtension, ViewScopeContext, ViewScopeManager, ViewScopeEventListener, BeanStorage, OmniViewHandler, OmniExternalContext, OmniExternalContextFactory

Annotation Type ViewScoped

Usage

Configuration