How to save and retrive view when it's needed

Question

My goal is to keep session size as small as possible. (Why?.. it's other topic). What I have is Phase listener declared in faces-config.xml

<lifecycle>
        <phase-listener>mypackage.listener.PhaseListener</phase-listener>   
</lifecycle>

I want to save all other views, except the last one(maximum two) , in some memcache. Getting the session map:

Map<String, Object> sessionMap = event.getFacesContext().getExternalContext().getSessionMap();

in beforePhase(PhaseEvent event) method is giving me access to all views. So here I could save all views to the memcache and delete them from the session. The question is where in jsf these views that are still loaded in the browser are requested so that I can refill with this view if it's needed. Is it possible at all? Thank you.

Answer 1

To address the core of your question, implement a ViewHandler, within which you can take control of the RESTORE_VIEW and RENDER_RESPONSE phases/processes. You'll save the view during the RENDER_RESPONSE and selectively restore, during the RESTORE_VIEW phase. Your view handler could look something like the following

   public class CustomViewHandlerImpl extends ViewHandlerWrapper{

        @Inject ViewStore viewStore; //hypothetical storage for the views. Could be anything, like a ConcurrentHashMap
        ViewHandler wrapped;

        public CustomViewHandlerImpl(ViewHandler toWrap){          
           this.wrapped = toWrap;
        }

        public UIViewRoot restoreView(FacesContext context, String viewId) throws IOException{

            //this assumes you've previously saved the view, using the viewId

            UIViewRoot theView = viewStore.get(viewId);

            if(theView == null){

               theView = getWrapped().restoreView(context, viewId);              
            }

           return theView;       
        } 


      public void renderView(FacesContext context, UIViewRoot viewToRender) throws IOException, FacesException{

          viewStore.put(viewToRender.getId(),viewToRender);

          getWrapped().renderView(context, viewToRender);

      }

   }

Simply plug in your custom viewhandler, using

<view-handler>com.you.customs.CustomViewHandlerImpl</view-handler>

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Of course, you probably don't want to give this treatment to all your views; you're free to add any conditions to the logic above, to implement conditional view-saving and restoration.

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You should also consider other options. It appears that you're conflating issues here. If your true concern is limit the overhead associated with view processing, you should consider

1. Stateless Views, new with JSF-2.2. The stateless view option allows you to exclude specific pages from the JSF view-saving mechanism, simply by specifying transient="true" on the f:view. Much cleaner than mangling the UIViewRoot by hand. The caveat here is that a stateless view cannot be backed by scopes that depend on state-saving, i.e. @ViewScoped. In a stateless view, the @ViewScoped bean is going to be recreated for every postback. Ajax functionality also suffers in this scenario, because state saving is the backbone of ajax-operations.

2. Selectively set mark components as transient The transient property is available for all UIComponents, which means, on a per-view basis, you can mark specific components with transient="true", effectively giving you the same benefits as 1) but on a much smaller scope. Without the downside of no ViewScoped

EDIT: For some reason, UIViewRoot#getViewId() is not returning the name of the current view (this might be a bug). Alternatively, you can use

ExternalContext extCtxt = FacesContext.getCurrentInstance().getExternalContext();
String viewName = ((HttpServletRequest)extCtxt.getRequest()).getRequestURI();  //use this id as the key to store your views instead