JSF + backing bean: How to detect when the application first load

How do I do something like this

Inside JSF file, list.xhtml

 <p:dataTable value="#{document.drawings}" var="item">
     //document is the backing bean that has method getDrawings() that return list of item
 </p:dataTable>  

Inside my backing bean, document.java

 List<Drawing> drawings;
 ...
 public void List<SelectItem> getDrawings(){
      if(application first load){
           return sessionB开发者_JAVA百科ean.getAllDrawings();
      }else{
           return drawings;
      }
 }

So the logic is that if the application first load, then load every thing from the datasource, by accessing method getAllDrawings() inside session bean, otherwise return drawings which is the list of Drawing that has been manipulate by some ajax method.

You can have a

@PostConstruct
public void init() { 
      drawings = loadDrawings();
}

But you can also have the so-called "lazy-loading". I.e.:

public void List<SelectItem> getDrawings(){
      if(drawings == null) {
           drawings = sessionBean.getAllDrawings();
      }
      return drawings;
}

Declare it as an application scoped bean and put the desired application-startup-initialization logic in its constructor. You can if necessary inject it as <managed-property> (or if you're already on JSF 2.0, as @ManagedProperty) in any other request/session scoped bean.

An application scoped bean is created only once and shared among all sessions/requests during webapplication's lifetime.