JSF without @ViewScoped

问题

I've been using JSF for many years and in the next project we're aiming to make the web-tier as stateless as possible. One possibility I'm exploring is removing @ViewScoped beans in favour of @RequestScoped (plus one or two @SessionScoped beans as required). This is proving troublesome for complex pages with AJAX, datatables and conditional rendering. My question is: how well does JSF (and PrimeFaces) work with stateless web beans? Is this something that I should continue to explore, or is @ViewScope now so fundamental that it's not worth the effort?

I appreciate as I write this question that it might be be closed as 'primarily opinion based', however I'm hoping that it isn't, I'm interested in specific problems that @ViewScope solved and what historic workarounds I'd have to re-introduce by ignoring @ViewScoped.

回答1:

How well does JSF (and PrimeFaces) work with stateless web beans?

It's technically possible.

JSF uses the view state primarily to keep track of the "disabled", "readonly" and "rendered" attributes of the UIInput and UICommand components as well as the "submitted value", "local value" and "is valid?" states of the EditableValueHolder components (implemented by among others UIInput).

In case of "disabled", "readonly" and "rendered" attributes, if these represent an EL expression, then JSF will re-check it during processing the form submit request. Below is a basic example:

<h:form>
    <h:commandButton value="toggle" action="#{bean.toggle}">
        <f:ajax render="panel" />
    </h:commandButton>
    <h:panelGroup id="panel">
        <h:commandButton value="submit" action="#{bean.submit}" rendered="#{bean.toggled}">
            <f:ajax />
        </h:commandButton>
    </h:panelGroup>
</h:form>

@Named
@ViewScoped
public class Bean implements Serializable {

    private static final long serialVersionUID = 1L;

    private boolean toggled;

    public void toggle() {
        this.toggled = !toggled;
    }

    public void submit() {
        System.out.println("Submitted");
    }

    public boolean isToggled() {
        return toggled;
    }
}

First click the "toggle" button and then the "submit" button. In case of a view scoped bean, it'll work just fine. If you however replace @ViewScoped by @RequestScoped here, then it'll fail, because toggled defaults back to false at the moment JSF needs to decode the "submit" button during the postback request, and so its rendered attribute will evaluate false and ultimately JSF won't queue the action event.

In such case, you need to make sure yourself that the property is preinitialized to the expected value during (post)construction of the request scoped bean. One way is to use hidden input fields for this within the ajax-updated component. Here's the adjusted example:

<h:form>
    <h:commandButton value="toggle" action="#{bean.toggle}">
        <f:ajax render="panel" />
    </h:commandButton>
    <h:panelGroup id="panel">
        <input type="hidden" name="toggled" value="#{bean.toggled}" />
        <h:commandButton value="submit" action="#{bean.submit}" rendered="#{bean.toggled}">
            <f:ajax />
        </h:commandButton>
    </h:panelGroup>
</h:form>

@Named
@RequestScoped
public class Bean {

    @Inject @ManagedProperty("#{param.toggled}")
    private boolean toggled;

    public void toggle() {
        this.toggled = !toggled;
    }

    public void submit() {
        System.out.println("Submitted");
    }

    public boolean isToggled() {
        return toggled;
    }
}

NOTE: a <h:inputHidden> will unfortunately not work as it updates the model value only after the action event is to be queued. Even not with a immediate="true" on it. This brings me by the way on the idea for a new <o:inputHidden> for OmniFaces.

With these changes, it'll work fine.

However, as the state which was originally view scoped (the toggled property) has now become a request parameter, it's fully exposed to the world and therefore also tamperable by hackers. Hackers wanting to invoke the "submit" button without invoking the "toggle" button first can now simply manually add a request parameter toggled=true. Whether that's desirable depends on the business requirements of your application, but more than often it's totally undesirable.

This is what JSF is trying to protect you from by offering the possibility to put these sensitive properties in a @ViewScoped bean instead.

This is proving troublesome for complex pages with AJAX, datatables and conditional rendering

True, but still not technically impossible. You only have to manually carry around the paginated, sorted and filtered states via manually populated hidden input fields as demonstrated above. The <p:dataTable> supports binding these states to bean properties. For example:

<p:dataTable ...
    first="#{bean.first}"
    sortField="#{bean.sortField}"
    sortOrder="#{bean.sortOrder}"
    filterBy="#{bean.filterBy}">
    ...
</p:dataTable>

You can just copy them into <input type="hidden"> fields as demonstrated before (which you make sure are covered by <p:ajax update>!) and finally grab them via @ManagedProperty and/or the @PostConstruct.

In effects, you're this way basically reinventing the job currently already done by javax.faces.ViewState hidden input field in combination with @ViewScoped beans. So why not using it right away? :)

If your primary concern is the memory usage, then you need to carefully design your beans in such way that only the view scoped state is stored in a @ViewScoped bean and that only the request scoped state is stored in a @RequestScoped bean. For instance, it's perfectly fine to put the data model in the request scoped bean and the paginated/sorted/filtered state in the view scoped bean. You may also want to consider OmniFaces @ViewScoped instead as that immediately destroys the view state and the physical bean when the page is unloaded.

That said, with this question in mind, I've just a few hours ago verified and improved the OptimusFaces library to ensure that it also fully supports stateless views with <f:view transient="true">, along with a new integration test. The advantage of OptimusFaces is among others that you don't anymore need to manually worry about carrying around the paginated/sorted/filtered state. OptimusFaces will worry about it for you.

JSF without @ViewScoped

问题

回答1:

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