Adding multiple conditions in required attribute and binding - jsf

Question

I want to create a JSF application.
Sorry for this over ambitious requirement.
In the application the user will have three drop downs.
Can we add multiple required conditions into one required attribute?
If a user selects the country Mexico / value 3 from the first drop down then he is required to choose the option Cancun / value 6 from the multiselect
Also If he selects the drop down value Continent North America He is required to choose the option of Chicago / value 2 from the multiselect
I have added the binding , required attribute for multiSelectListbox for multiple required options but they are not triggered when the drop down is selected
<h:form>
<p:growl id="msgs" showDetail="true" skipDetailIfEqualsSummary="true" />
<p:panel header="Tranfer Destination" style="margin-bottom:10px;">
<h:panelGrid columns="2" cellpadding="5">
<p:outputLabel for="country" value="Country: " />
<p:selectOneMenu id="country" value="#{dropdownView.country}" style="width:150px" required="true" binding="#{country}">
<f:selectItem itemLabel="Select Country" itemValue="" noSelectionOption="true" />
<f:selectItems value="#{dropdownView.countries}" />
<p:ajax update="city"/
</p:selectOneMenu>
<p:outputLabel for="Continent" value="Continent: " />
<p:multiSelectListbox id="continent" value="#{dropdownView.continent}" style="width:150px" required="true" binding="#{continent}">
<f:selectItem itemLabel="Select Continent" itemValue="" noSelectionOption="true" />
<f:selectItem itemLabel="Asia" itemValue="1"> </f:selectItem>
<f:selectItem itemLabel="Europe" itemValue="2"> </f:selectItem>
<f:selectItem itemLabel="South America" itemValue="3"> </f:selectItem>
<f:selectItem itemLabel="North America" itemValue="4"> </f:selectItem>
<f:selectItem itemLabel="Africa" itemValue="5"> </f:selectItem>
<p:ajax update="city"/
</p:multiSelectListbox>
<p:outputLabel for="city" value="City: " />
<p:multiSelectListbox id="city" value="#{dropdownView.city}" style="width:150px" required="#{(not empty param[country.6]) (not empty param[continent.4])}">
<f:selectItem itemLabel="Select City" itemValue="" noSelectionOption="true" />
<f:selectItem itemLabel="New York" itemValue="1"> </f:selectItem>
<f:selectItem itemLabel="Chicago" itemValue="2"> </f:selectItem>
<f:selectItem itemLabel="Seattle" itemValue="3"> </f:selectItem>
<f:selectItem itemLabel="Toronto" itemValue="4"> </f:selectItem>
<f:selectItem itemLabel="Ontario" itemValue="5"> </f:selectItem>
<f:selectItem itemLabel="Cancun" itemValue="6"> </f:selectItem>
<f:selectItem itemLabel="Tijuana" itemValue="7"> </f:selectItem>
</p:multiSelectListbox>
</h:panelGrid>
<p:separator />
<p:commandButton value="Submit" update="msgs" action="#{dropdownView.displayLocation}" icon="pi pi-check" />
</p:panel>
</h:form>
List of Countries are populated from the database
ID NAME
1 USA-C
2 Canada-N
3 Mexico-C
The option Cancun / value 6 is required from the third drop down only If the user selects the country Mexico / value 3 from the first drop down.
The option Chicago / value 2 is required from the third drop down only If the user selects the continent North America / value 4 from the second drop down.
Other cities are optional for selection

Answer 1

If I have to do this, I won't use the required attribute and I will create a custom validator that checks the option selected on the first and second dropdown, and look if the third dropdown have the required values for the previous selection.
https://www.primefaces.org/showcase/ui/csv/custom.xhtml