How to get query parameters in ExceptionHandler? - exception

Question

In our project (JBoss 7.0.2, JSF 2), we work on a solution to catch all exceptions during user navigation and redirect them to nice error pages.
I used an ExceptionHandler, inspired by a lot of examples and tutorials online.
I managed to do a redirection feature without too much difficulty: in the ExceptionHandler.handle() method, for some exceptions (expired view/session, unauthenticated user asking a denied page, ...) I redirect the user on the login page through a good old
FacesContext.getCurrentInstance().getExternalContext().redirect(myRedirectPage);
with an additional query parameter containing the original url base64 encoded, and after a successful authentication I use the same redirection mechanism to send the user back to their page.
The problem is with ViewExpiredException on JSF actions, by example when the user click after their view has expired on any button or link with action or actionListener, synchronous or ajax-style, like
<h:commandButton action="#{myBean.myAction}" value="do that" />
or
<h:commandLink value="do that too">
<f:ajax render=":aZone" execute="#form" listener="#{myBean.myOtherAction}" />
</h:commandLink>
I cannot manage to obtain the query parameters in my ExceptionHandler.handle() method.
I tried to put my parameters in a f:metadata section, like
<f:metadata>
<f:viewParam name="myParam" value="#{myBean.myParam}" />
</f:metadata>
and to include them in the action, so in the method bound to button action I returned
"myPage.xhtml?includeViewParams=true"
but it changed nothing :-/
Am I doing something wrong? Where am I supposed to find the query paremeters? Is it in
FacesContext.getCurrentInstance().getExternalContext().getRequest()
** UPDATE **
As said in comments, view params are no more available after a ViewExpiredException (quite obvious, in fact), so params are to be stored elsewhere (#BalusC quickly suggested in a request scope or through cookie).

Answer 1

The request parameters are available by ExternalContext#getRequestParameterMap().
Map<String, String> params = externalContext.getRequestParameterMap();
// ...
Or if your application uses same parameter name with multiple values (which is usually the case for <h:selectManyXxx> components), use ExternalContext#getRequestParameterValuesMap() instead
Map<String, String[]> params = externalContext.getRequestParameterValuesMap();
// ...
Please note that this only returns the parameters of the current request, not of the initial request in case of postbacks.
As to the ExternalContext#getRequest(), it returns in case of JSF applications running on a servlet container an instance of HttpServletRequest which you'd need to cast, but you should rarely have the need to get it. The ExternalContext, while following the Facade design pattern, has a lot of methods which are delegating to the underlying raw HTTP servlet request, session and context. You'd namely ultimately like to end up with zero javax.servlet imports in your backing beans.
Update as per your comment, you actually want to get only the view parameters which are been registered by <f:viewParam>. You can get them by ViewMetadata#getViewParameters() wherein you pass the current UIViewRoot.
Collection<UIViewParameter> viewParameters = ViewMetadata.getViewParameters(FacesContext.getCurrentInstance().getViewRoot());
// ...