SelectOneMenu updates other SelectOneMenu [duplicate]

Answer 1

Primefaces has a great feature of what you trying to achieve. It already using Ajax, so don't have to worry about writing code your self.

Answer 2

Actually you can use a ValueChangeListener that is invoked when the value of your selectOneMenu changes:

<h:selectOneMenu class="category" valueChangeListener="#{yourBean.selectOneMenuListener}">
    <f:selectItems value="#{categoryBackingBean.categorys}" var="c"
        itemLabel="#{c.category_Name}" itemValue="#{c.id}" />
</h:selectOneMenu>

Then, in your bean you have this method:

public void selectOneMenuListener(ValueChangeEvent event) {
    //This will return you the newly selected
    //value as an object. You'll have to cast it.
    Object newValue = event.getNewValue(); 
    //The rest of your processing logic goes here...
}

To update the page you can either add onchange="submit()" to your <h:selectOneMenu/>. For some partial rendering you can try adding this <f:ajax/> instead of onchange="submit()":

<h:selectOneMenu class="category" valueChangeListener="#{yourBean.selectOneMenuListener}">
    <f:selectItems value="#{categoryBackingBean.categorys}" var="c"
        itemLabel="#{c.category_Name}" itemValue="#{c.id}" />
    <f:ajax event="change" execute="@form" render="theIdOfTheComponentYouWantToReRender"/>
</h:selectOneMenu>

If I'm not mistaken you'll want to get the id of the element selected in the first menu and populate the second one according to it. Then you can render the other selectOneMenu or, if needed, a panel wrapping a part of your form.