OmniFaces & JSF Fans: JSF Scopes Tutorial - DeltaSpike View Access Scope (and View Scope)

OmniFaces is an utility library for JSF, including PrimeFaces, RichFaces, ICEfaces ...
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joi, 12 noiembrie 2015

JSF Scopes Tutorial - DeltaSpike View Access Scope (and View Scope)

The DeltaSpike view access scope ensures beans with a lifetime which is
as long as needed and as short as possible - which are terminated automatically (as soon as possible)

The DeltaSpike view scope provides a CDI context for the JSF 2.0/2.1

The view scope is useful when you need to preserve data over multiple requests without leaving the current JSF view by clicking on a link, returning a different action outcome, or any other interaction that dumps the current view. This means that such beans cannot live in a conversation which involves multiple views (pages). By the other hand, when a conversation ends, the beans are not destroyed immediately (by default, they will continue to exist until the container decide to destroy them (e.g. timeout)). The DeltaSpike view access scope increases the lifespan of the view scope to control beans lifespan over multiple pages. Basically, this scope keeps a bean available as long as it is referenced from a page and make it available for the next page. If the next page doesn't use (access) this bean then it is destroyed. At a further use, it will be recreated. Practically, as long as you keep a bean in a conversation it will be alive. It is important that it is based on the view-id of a page, not on the request.

View Access Scope Annotations

The DeltaSpike view access scope annotation is @ViewAccessScoped (org.apache.deltaspike.core.api.scope.ViewAccessScoped). A bean with this scope should be annotated with @Named (javax.inject.Named).

Simple example

First we write a simple bean, DSViewScopedBean annotated with @ViewAccessScoped and with several simple methods. Among this methods we have a @PostConstruct and a @PreDestroy methods that will signal when instances of DSViewScopedBean are created (initialized) and destroyed:

package beans;

import java.io.Serializable;

import java.util.logging.Logger;

import javax.annotation.PostConstruct;

import javax.annotation.PreDestroy;

import javax.inject.Named;

import org.apache.deltaspike.core.api.scope.ViewAccessScoped;

@Named(value = "dsViewScoped")

@ViewAccessScoped

public class DSViewScopedBean implements Serializable {

private static final Logger LOG = Logger.getLogger(DSViewScopedBean.class.getName());

private final String done;

public DSViewScopedBean() {

done = "Done!";

}

@PostConstruct

public void init() {

LOG.info("DSViewScopedBean#init() invoked ...");

}

// forward to the same view

public void action() {

LOG.info("DSViewScopedBean#action() invoked ...");

}

// forward to the done_static.xhtml page

public String actionStaticOutcome() {

LOG.info("DSViewScopedBean#actionStaticOutcome() invoked ...");

return "done_static";

}

// forward to the done_dynamic.xhtml page

public String actionDynamicOutcome() {

LOG.info("DSViewScopedBean#actionDynamicOutcome() invoked ...");

return "done_dynamic";

}

// redirect to the done_static.xhtml page

public String actionRedirectStaticOutcome() {

LOG.info("DSViewScopedBean#actionRedirectStaticOutcome() invoked ...");

return "done_static?faces-redirect=true;";

}

// redirect to the done_dynamic.xhtml page

public String actionRedirectDynamicOutcome() {

LOG.info("DSViewScopedBean#actionRedirectDynamicOutcome() invoked ...");

return "done_dynamic?faces-redirect=true;";

}

@PreDestroy

public void destroy() {

LOG.info("DSViewScopedBean#destroy() invoked ...");

}

public String getDone() {

return done;

}

Now, the done_static.xhtml page is a very simple page that displays a static text - we will use this page to break down the conversation that uses (access) the above bean. Practically, when we navigate to this page the above bean should be destroyed immediately:

<?xml version='1.0' encoding='UTF-8' ?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"

xmlns:h="http://xmlns.jcp.org/jsf/html"

xmlns:ds="http://deltaspike.apache.org/jsf">

<h:head>

<title>DS @ViewAccessScoped</title>

</h:head>

<h:body>

<ds:windowId/>

Done!

</h:body>

</html>

Further, we have the done_dynamic.xhtml page. This page uses the above bean, and it will be a part of our conversation. So, when we navigate to this page, we expect to have the same instance of the bean available (as long as the bean exist in the current page). In addition this page has a link to the done_static.xhtml page, which doesn't use (access) the bean. When this link is clicked we practically end the conversation:

<?xml version='1.0' encoding='UTF-8' ?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"

xmlns:h="http://xmlns.jcp.org/jsf/html"

xmlns:ds="http://deltaspike.apache.org/jsf">

<h:head>

<title>DS @ViewAccessScoped</title>

</h:head>

<h:body>

<ds:windowId/>

#{dsViewScoped.done}<br/>

<h:link outcome="done_static">Done static</h:link>

</h:body>

</html>

The current (start) page is index.xhtml, and is very simple:

<?xml version='1.0' encoding='UTF-8' ?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"

xmlns:h="http://xmlns.jcp.org/jsf/html"

xmlns:ds="http://deltaspike.apache.org/jsf"

xmlns:f="http://xmlns.jcp.org/jsf/core">

<h:head>

<title>DS @ViewAccessScoped</title>

</h:head>

<h:body>

<ds:windowId/>

<h:form>

<h:panelGrid columns="1">

<h:commandButton value="DS View Access Scoped Bean" action="#{dsViewScoped.action()}"/>

<h:commandButton value="DS View Access Scoped Bean (Done static)" action="#{dsViewScoped.actionStaticOutcome()}"/>

<h:commandButton value="DS View Access Scoped Bean (Done dynamic)" action="#{dsViewScoped.actionDynamicOutcome()}"/>

<h:commandButton value="DS View Access Scoped Bean (Redirect done static)" action="#{dsViewScoped.actionRedirectStaticOutcome()}"/>

<h:commandButton value="DS View Access Scoped Bean (Redirect done dynamic)" action="#{dsViewScoped.actionRedirectDynamicOutcome()}"/>

</h:panelGrid>

</h:form>

<h:link outcome="done_static">Done static</h:link><br/>

<h:link outcome="done_dynamic">Done dynamic</h:link>

</h:body>

</html>

Now, let's see what happens when we press each of these buttons and links:

1. Press the button labeled "DS View Access Scoped Bean" few times

The application will navigate in the same page again and again and the output reveals that JSF will create a single instance of DSViewScopedBean, which is not destroyed during pressing this button: