Redirecting before rendering the page, if some condition

[ericjava.eric.chiralsoftware.net]

Here's my simple example: I have a page which displays invoices.  Call it /protected/show-invoice.xhtml.  It gets the Invoice object which it needs from the conversation context.

If there is no Invoice in the conversation, like if the user types in http://example.com/protected/show-invoice.seam, the page really shouldn't display at all because it will be completely broken.  In fact, it should simply bounce the user straight to a search for an invoice page or something like that.

I tried to do this with pages.xml:

    <page view-id="/protected/show-invoice.xhtml">
        
        <navigation>
            <rule if="#{true}">
                <redirect view-id="/protected/invoice-search.xhtml"/>
            </rule>
        </navigation>
    </page>
    

Note that I put in if="#{true}" which you would obviously not use in a real application.  I put that in there to force it to always trigger, so with that rule in place, it should never display but should always bounce straight to the invoice-search page.

But that doesn't work.  The navigation rule isn't triggering when it is from a GET request (ie, the user types that in to his browser URL field).

Is there a way to do this?  I'm aware of the <restrict> thing, but that's really for security checks, not for navigation.  I know that I can specify actions, which are method bindings which get called before the page is rendered.  But method bindings don't have a way to do a redirect; they are not Servlets.

How do I do this the Seam way?

Thanks

[ericjava.eric.chiralsoftware.net]

I searched around some more after asking, and found this page with a handy trick:

Redirect before rendering

In essence, you create a dummy action, which can in fact be a true noop:

@Name("helpfulPojo") public class HelpfulPojo {
  public void noop() { }
}

And then in pages.xml you do a trick like this:

    <page action="#{helpfulPojo.noop}" view-id="/protected/show-invoice.xhtml">
        
        <navigation from-action="#{helpfulPojo.noop}">
            <rule if="#{true}">
                <redirect view-id="/protected/invoice-search.xhtml"/>
            </rule>
        </navigation>
        
    </page>

And obviously, you would use some EL expression that's more meaningful than if="#{true}".

It works!  The action attribute's method binding gets called before rendering, and that then hits the navigation rule because of the from-action attribute on it.

Note the use of <redirect>, not a navigate-to or something like that.