How to load and display dependent h:selectOneMenu on change of a h:selectOneMenu

You can use <f:ajax> for this. When nested in an input component such as <h:selectOneMenu>, then it will by default be invoked when the input value is changed. You can specify a listener method which could prepopulate the data for the next component based on the current input value, and you can specify the client ID of that next component in render in order to show the prepopulated data.

<h:selectOneMenu value="#{bean.country}">
    <f:selectItems value="#{bean.countries}" />
    <f:ajax listener="#{bean.changeCountry}" render="cities" />
</h:selectOneMenu>
<h:panelGroup id="cities">
    <h:selectOneMenu value="#{bean.city}" rendered="#{not empty bean.cities}">
        <f:selectItems value="#{bean.cities}" />
    </h:selectOneMenu>
</h:panelGroup>

The bean must be in at least the view scope (not request):

@ManagedBean
@ViewScoped
public class Bean implements Serializable {

    private String country; // +getter+setter
    private String city; // +getter+setter
    private List<String> countries; // +getter
    private List<String> cities; // +getter

    @EJB
    private LocationService locationService;

    @PostConstruct
    public void init() {
        countries = locationService.getCountries();
    }

    public void changeCountry() {
        cities = locationService.getCities(country);
    }

    // ...
}

You can of course also use a Map<String, String> instead of a List<String>. The map key becomes the option label and the map value becomes the option value. You only need to keep in mind that a HashMap is by nature unordered. You'd prefer using LinkedHashMap instead to display the items in Map insertion order.

See also:

• Our selectOneMenu wiki page
• When to use valueChangeListener or f:ajax listener?