Question

I tried to use view parameters in conjunction with a request scoped bean. I noticed that the model does get updated and when the page is rendered, the bean properties are set and are rendered with <h:outputText value="myBean.myParameter />. My question is, about the post back. I was under the impression that the view parameter values were retained as long as you don’t post to a different view. I expected that the property would be set in the bean during the action method call automatically, but in practice I found this is not the case. Can someone explain why this is the case. I searched all around and I found many articles discussing viewParams but I couldn’t find an explanation of exactly what the effect is (and why) in each scope. If anyone knows of an article that documents this already can you point me to it. Thanks in advance…

Answer 1

I was under the impression that the view parameter values were retained as long as you don’t post to a different view.

This is only true when you’re using a view scoped bean because they are remembered in the bean. The view scoped bean lives as long as you’re interacting with the same view. I think that you’re confusing the request scope with the view scope, given your impression.

A request scoped bean is trashed by end of the HTTP request/response cycle. So when the webbrowser is finished loading the page, the request scoped backing bean is already trashed for long. When you submit a form on that page, a new request scoped bean will be created, the <f:viewParam> will check if the to-be-set request parameters are available and if not, then just skip it (or validate; if you have required="true" set on them). As long as you don’t retain view parameters by using <f:param> inside command links/buttons of the form on that page, then those parameters will get lost on subsequent requests and thus also in any involved request scoped bean.

See also:

• Communication in JSF 2.0