Prevent navigation when error occurs

Question

I have a use case where an error may occur during the INVOKE_APPLICATION phase. If it does, I need to stay on the same page and show the user the error. I am using a PhaseListener to detect the error (in the afterPhase of the INVOKE_APPLICATION phase). If there is an error, I show it to the user by calling FacesContext.getCurrentInstance().addMessage(null, errorMessage);. This works. The problem is, it continues navigation to the next view. For example, if the user clicked the Save button and that button returns to the previous page, I want the user to stay on this page if there is an error. I tried calling FacesContext.getCurrentInstance().renderResponse() to bypass the navigation, but that didn't work. Then I tried calling FacesContext.getCurrentInstance().responseComplete();. This did bypass navigation, but the error didn't show up for the user to see.
This seems like a common use case, so I must be missing some obvious way to do this.
Thanks for your help!
Cheers,
Mike

Answer 1

Hi,
What kind of error? When does it happen exactly? I doubt PhaseListener will be the best solution. Assuming it is for the purpose of this post, however, it would be:
private static final ThreadLocal<UIViewRoot> root = new ThreadLocal<UIViewRoot>();
public void beforePhase(PhaseEvent ev)
    root.set(ev.getFacesContext().getViewRoot());
public void afterPhase(PhaseEvent ev)
    try
        if (detectError())
            FacesContext context = ev.getFacesContext();
            // Add message
            UIViewRoot originalRoot = root.get();
            UIViewRoot newRoot = context.getViewRoot();
            if (newRoot != originalRoot)
                context.setViewRoot(originalRoot);
            // Another option would be to always call context.setViewRoot(originalRoot); as if it's the same then it won't have any effect.
    finally
        root.remove();
}Regards,
~ Simon