<h:form id="form">
  <h:selectOneMenu id="country"
      value="#{test.country}"
      valueChangeListener="#{test.changeCountry}">
    <f:selectItems value="#{test.countryItems}"/>
    <f:ajax render="state"/>
  </h:selectOneMenu>
  <h:selectOneMenu id="state" value="#{test.state}">
    <f:selectItems value="#{test.stateItems}"/>
  </h:selectOneMenu>
</h:form>