<h:form>
        <p:panelGrid>
            <p:row>
                <p:column>
                    <p:outputLabel for="departureRegion" value="Please select a departure region:"/>
                </p:column>
                <p:column>
                    <p:selectOneMenu id="departureRegion" value="#{flightBean.departureRegion}">
                        <f:selectItems value="#{flightBean.allRegions}" var="region" itemValue="#{region}"
                                       itemLabel="#{region.name}"/>
                        <f:ajax render="departureLocation"/>
                    </p:selectOneMenu>
                </p:column>
            </p:row>
             <p:row>
                 <p:column>
                     <p:outputLabel for="departureLocation" value="Please select a departure location: "/>
                 </p:column>
                 <p:column>
                    <p:selectOneMenu id="departureLocation" value="#{flightBean.departureLocation}">
                        <f:selectItems value="#{flightBean.allLocationsByRegion}" var="location" itemValue="#{location}"
                                       itemLabel="#{location.name}"/>
                    </p:selectOneMenu>
                 </p:column>
             </p:row>
        </p:panelGrid>
    </h:form>

@ManagedBean
@ViewScoped
public class FlightBean implements Serializable{
    @EJB
    private LocationService locationService;

    @EJB
    private RegionService regionService;

    @NotNull
    private Location departureLocation;

    private Region departureRegion;

    private Logger logger = LoggerFactory.getLogger(FlightBean.class);

    public FlightBean() {

    }

    @PostConstruct
    public void init(){
        this.departureRegion = regionService.findRegionById(1);
    }

    public Location getDepartureLocation() {
        return departureLocation;
    }

    public void setDepartureLocation(Location departureLocation) {
        this.departureLocation = departureLocation;
    }

    public Region getDepartureRegion() {
        return departureRegion;
    }

    public void setDepartureRegion(Region departureRegion) {
        logger.info("region is " + departureRegion);
        this.departureRegion = departureRegion;
    }

    public List<Region> getAllRegions(){
        return regionService.findAllRegions();
    }

    public List<Location> getAllLocationsByRegion(){
        return locationService.findAllLocationsByRegion(departureRegion);
    }

    public void refreshLocations(AjaxBehaviorEvent event){
        logger.info("event " + event.toString());
        getAllLocationsByRegion();
    }
}