Put the bean in the view scope and get rid of any business logic in getter methods.
The bean must be placed in the view scope so that all previous selections and new available items are remembered for subsequent postbacks, otherwise things will fail when JSF needs to validate the selected item against the list of available items which was prepopulated in a previous selection, or when e.g. rendered attribute depends on a condition which was only set in a previous request.
The getter methods may not contain any business logic as they will also be invoked during among others the validations phase. You should use <f:ajax listener>/<p:ajax listener> to perform business logic based on a change. You should in the listener method also explicitly clear out selected values of child selection components. You can use <f:ajax render>/<p:ajax update> to update the contents of child selection components.
Thus, so:
<h:selectOneMenu id="state" value="#{nodes.selectedState}">
<f:selectItem itemValue="#{null}" itemLabel="-- select --" />
<f:selectItems value="#{nodes.availableStates}" />
<f:ajax listener="#{nodes.changeState}" render="city region station" />
</h:selectOneMenu>
<h:selectOneMenu id="city" value="#{nodes.selectedCity}">
<f:selectItem itemValue="#{null}" itemLabel="-- select --" />
<f:selectItems value="#{nodes.availableCities}" />
<f:ajax listener="#{nodes.changeCity}" render="region station" />
</h:selectOneMenu>
<h:selectOneMenu id="region" value="#{nodes.selectedRegion}">
<f:selectItem itemValue="#{null}" itemLabel="-- select --" />
<f:selectItems value="#{nodes.availableRegions}" />
<f:ajax listener="#{nodes.changeRegion}" render="station" />
</h:selectOneMenu>
<h:selectOneMenu id="station" value="#{nodes.selectedStation}">
<f:selectItem itemValue="#{null}" itemLabel="-- select --" />
<f:selectItems value="#{nodes.availableStations}" />
</h:selectOneMenu>
with
@Named
@ViewScoped
public class Nodes {
private String selectedState; // getter+setter
private String selectedCity; // getter+setter
private String selectedRegion; // getter+setter
private String selectedStation; // getter+setter
private List<SelectItem> availableStates; // getter (no setter necessary!)
private List<SelectItem> availableCities; // getter (no setter necessary!)
private List<SelectItem> availableRegions; // getter (no setter necessary!)
private List<SelectItem> availableStations; // getter (no setter necessary!)
@EJB
private SomeService someService;
@PostConstruct
public void init() {
availableStates = someService.listStates();
}
public void changeState(AjaxBehaviorEvent event) {
availableCities = someService.listCities(selectedState);
selectedCity = selectedRegion = selectedStation = null;
availableRegions = availableStations = null;
}
public void changeCity(AjaxBehaviorEvent event) {
availableRegions = someService.listRegions(selectedCity);
selectedRegion = selectedStation = null;
availableStations = null;
}
public void changeRegion(AjaxBehaviorEvent event) {
availableStations = someService.listStations(selectedRegion);
selectedStation = null;
}
// Generate necessary getters+setters here. You should not change them.
}