Make multiple dependent / cascading selection components in JSF - jsf

Question

I am trying to make 4 dependent / cascading selection components. In this question, the selection component happens to be a <h:selectOneMenu>, but this is of course applicable on any other kind of selection component extending from UISelectOne/UISelectMany superclass, such as <h:selectManyCheckbox> or PrimeFaces <p:selectCheckboxMenu>, <p:selectManyMenu>, etc.
When the user chooses an item from the first menu, the second menu will show dependent data and when the user chooses item from the second one , the third one will show dependent data and so on.
The user will see items on the first menu only and the other ones will be blank. If he chooses an item on the first menu the second one will show data but the third and the fourth will remain blank, and so on. The user must eventually choose entries from all the 4 menus.
<h:selectOneMenu id="first" value="#{nodes.selectState}">
<f:selectItems value="#{nodes.stateList}"/>
<f:ajax render="second">
</h:selectOneMenu>
<h:selectOneMenu id="second" value="#{nodes.selectCity}">
<f:selectItems value="#{nodes.cityList}"/>
<f:ajax render="third">
</h:selectOneMenu>
<h:selectOneMenu id="third" value="#{nodes.selectRegion}">
<f:selectItems value="#{nodes.regionList}"/>
<f:ajax render="fourth">
</h:selectOneMenu>
<h:selectOneMenu id="fourth" value="#{nodes.selectStation}">
<f:selectItems value="#{nodes.stationList}"/>
</h:selectOneMenu>
Nodes bean
private String selectState; //+setters, getters
private String selectCity; //+setters, getters
private String selectRegion; //+setters, getters
private String selectStation; //+setters, getters
private List<SelectItem> stateList; //+setters, getters
private List<SelectItem> cityList; //+setters, getters
private List<SelectItem> regionList; //+setters, getters
private List<SelectItem> stationList; //+setters, getters
public getStateList(){
stateList= new ArrayList<SelectItem>();
stateList.add(new SelectItem("A"));
}
public getCityList(){
CityList= new ArrayList<SelectItem>();
if(selectState.equals("A")){
CityList.add(new SelectItem("B"));
}
}
public getRegionList(){
RegionList= new ArrayList<SelectItem>();
if(selectCity.equals("B")){
RegionList.add(new SelectItem("C"));
}
}
public getStationList(){
StationList= new ArrayList<SelectItem>();
if(selectRegion.equals("C")){
StationList.add(new SelectItem("D"));
}
}
It's only working for the first 2 menus. The other 2 menus get null values.

Answer 1

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.
}
See also:
How to choose the right bean scope?
Best way to add a "nothing selected" option to a selectOneMenu in JSF
How to populate options of h:selectOneMenu from database?
When to use valueChangeListener or f:ajax listener?
Why JSF calls getters multiple times

Answer 2

Try this, it may help you
By using the --Select City-- , --Select Region--, --Select Station-- to avoid the null pointer Exception.
public getStateList(){
stateList= new ArrayList<SelectItem>();
stateList.add(new SelectItem("A"));
}
public getCityList(){
CityList= new ArrayList<SelectItem>();
if(selectState.equals("A"))
{
CityList.add(new SelectItem("B"));
}
else
{
CityList.add(new SelectItem("--Select City--"));
selectCity = "--Select City--";
}
public getRegionList(){
RegionList= new ArrayList<SelectItem>();
if(selectCity.equals("B"))
{
RegionList.add(new SelectItem("C"));
}
else
{
RegionList.add(new SelectItem("--Select Region--"));
selectRegion = "--Select Region--";
}
}
public getStationList(){
StationList= new ArrayList<SelectItem>();
if(selectRegion.equals("C"))
{
StationList.add(new SelectItem("D"));
}
else
{
StationList.add(new SelectItem("Select Station"));
selectStation = "--Select Station--";
}
}

Answer 3

There is a typo error in your code. For third menu you have given id name as "first" instead of "third". May be its because of that problem.

Answer 4

You are facing this issue because you have twice id="first".
Fix this and it should work.