Removing @ViewScoped beans in a SPA JSF 2.2 application

Question

We are using an SPA approach in our JSF 2.2 + PrimeFaces enabled application. The basic idea was originally described very well here:

Refreshing dynamic content with AJAX in JSF using SPA approach

But, as we know, using this SPA approach has a drawback when using @ViewScoped beans.

As we are actually always staying in the same JSF View, @ViewScoped beans are not removed from memory, when we replace the content of a panel group with the new SPA content.

I have found a solution, but I would like to know if it's a correct approach, and/or if there is anything missing.

Basically, in our NavigationService bean, which holds the name of the page to be rendered during the SPA AJAX request, we always execute the following code:

private void clearViewScopedBeans() {
    Map<String, Object> viewMap = FacesContext.getCurrentInstance().getViewRoot().getViewMap();
    for(Iterator<Map.Entry<String, Object>> it = viewMap.entrySet().iterator(); it.hasNext(); ) {
      Map.Entry<String, Object> entry = it.next();
      it.remove();    
    }
}

This should ensure that, after the new SPA snippet is rendered, all the previous existing @ViewScoped beans are removed.

However, I think the above code only removes the View Scoped beans, but not the related View States. Is that correct ?

I found an old blog entry which seems to do a little more logic: http://javaevangelist.blogspot.sg/2014/08/jsf-21-tip-of-day-clearing-viewscope.html

but I dunno if it's correct as well.

Additionally, if we want to support multiple window tabs, our NavigationService bean, holding the current SPA snippet page name, must be @ViewScoped as well, and this introduces a small problem:

When running the above code for removing all the existing @ViewScoped beans... we have to exclude the NavigationService bean itself !! Otherwise we end up loading always the same page, because a new instance of the NavigationService is instantiated, with a default SPA page name, instead of the new one.

So, all in all, our code looks finally like this, where we keep a Map of "excluded" bean names, that we don't want to remove on a SPA page refresh (namely the NavigationService bean holding the SPA page name)

    private void clearViewScopedBeans() {
    Map<String, Object> viewMap = FacesContext.getCurrentInstance().getViewRoot().getViewMap();
    for(Iterator<Map.Entry<String, Object>> it = viewMap.entrySet().iterator(); it.hasNext(); ) {
      Map.Entry<String, Object> entry = it.next();
      if(!exclusionViewScopedBeans.contains(entry.getKey())) {
          logger.info("Removing an instance of a @ViewScoped bean -> " + entry.getKey());
        it.remove();
      }
    }
}

Now the question ... is this the correct approach for handling these kind of SPA situations? Are we missing something here?

Any feedback would be greatly appreciated... thanks a lot in advance !

Thats the implementation I used - in terms of correct approach I the impression i get is that you should avoid this kind of thing in JSF, but the reality is sometimes you need to — farrellmr
Because this particular project uses Spring IoC instead of CDI... so no built-in Conversation scope so far. :( In any case, I'm also looking into creating new (Spring) Scopes that can achieve the same functionality. So far, I have successfully created a TabScope for PrimeFaces TabView component. Each Tab can have its own scope of JSF beans, created when the tab is constructed, and destroyed when the tab is closed. I guess I could use the same approach to develop a more generic Conversation Scope ... — Maikel Nait

Radek Radek · Accepted Answer · 2017-10-05T14:34:19

I think, there is no better solution for removing/clearing ViewScopedBeans in SPA (single page app) than yours Maikel:

private void clearViewScopedBeans() {
Map<String, Object> viewMap = FacesContext.getCurrentInstance().getViewRoot().getViewMap();
for(Iterator<Map.Entry<String, Object>> it = viewMap.entrySet().iterator(); it.hasNext(); ) {
  Map.Entry<String, Object> entry = it.next();
  it.remove();    
}
}

I have tried find a lot, but SPA is not "official recommended" way of using JSF, that is multi-page app, so SPA requires more fiddling around with.

Or, Maikel, have you found or do you use something another way?

Removing @ViewScoped beans in a SPA JSF 2.2 application

1 Answers