Loading h:selectOneMenu depending of another h:selectOneMenu value - jsf

Question

I have two h:selectOneMenu (1: Countries, 2: Cities). I need to load all cities from one selected country in the cities selectOneMenu using ajax. When I change the value of the countries selectOneMenu my cities selectOneMenu takes a null value from countryBean.selectedCountry.
<h:panelGrid columns="2">
<h:outputLabel for="countries" value="Countries: " />
<h:selectOneMenu converter="omnifaces.SelectItemsConverter"
id="countries" required="true" value="#{countryBean.selectedCountry}">
<f:selectItem itemLabel="Choose country" />
<f:selectItems value="#{countriesBB.findAllCountries()}"
var="country" itemLabel="#{country.name}" />
<f:ajax event="change" render="cities" />
</h:selectOneMenu>
<h:outputLabel for="cities"
value="Cities: " />
<h:selectOneMenu converter="omnifaces.SelectItemsConverter"
id="cities" required="true"
value="#{cityBean.selectedCity}">
<f:selectItem itemLabel="Choose city" />
<f:selectItems value="#{cityBean.findAllCitiesByCountry(countryBean.selectedCountry)}"
var="city" itemLabel="#{city.name}" />
</h:selectOneMenu>
</h:panelGrid>
This is the method that find the cities:
public List<city> findAllCitiesByCountry(Country country) {
List<City> cities = null;
try {
cities = citiesService.findAllCitiesByCountry(country);
} catch (Exception exception) {
logger.debug("Error finding cities.", exception);
}
return cities;
}
I am getting a NullPointerException because countryBean.selectedCountry is always null. What is the right way to do this?

Answer 1

One of the many rules which a JSF starter need to know:
Don't do business logic in a getter method.
Once you try to fix that by keeping your getter methods true getter methods (i.e. do not do anything else than just return property;) and performing the business logic in (post)constructor and/or action(listener) methods, then this particular problem shall disappear.
Here's a kickoff example:
<h:selectOneMenu value="#{bean.country}">
<f:selectItems value="#{bean.countries}" ... />
<f:ajax listener="#{bean.changeCountry}" render="cities" />
</h:selectOneMenu>
<h:selectOneMenu id="cities" value="#{bean.city}">
<f:selectItems value="#{bean.cities}" ... />
</h:selectOneMenu>
With something like this in a #ViewScoped bean:
private Country country; // +getter+setter
private City city; // +getter+setter
private List<Countries> countries; // +getter
private List<Cities> cities; // +getter
#EJB
private SomeService service;
#PostConstruct
public void init() {
countries = service.getCountries();
}
public void changeCountry() {
cities = service.getCities(country);
}