JSF 1.2 and getting selected value from dropdown

JSF 1.2 has some weird features which you just have to know if you haven’t read the documents. One example is getting a value from h:selectOneMenu dropdown after onchange event. The first what comes to mind is to use binding attribute with RichFaces’ a4j:support for rerendering elements after the event but it doesn’t work like you thought it would. In some cases using the binding attribute works just fine but as the binding attribute should refer to a request scoped bean property, not a session scoped one, you might get “Duplicate id error” when switching pages back and forth.

Fortunately there is valueChangeListener in h:SelectOneMenu which you can trick to do almost the same. It is executed during Validations phase, before the “Update Model Values” phase and is intended to get a handle of both the old and new value so that you can do some business stuff based on the real change. However, you can use it to invoke actions on a dropdown change only by combining it with onchange="submit()" and immediate="true" and the selected value is to be obtained by ValueChangeEvent#getNewValue(). (StackOverflow, BalusC)

For example:

Jspx:
<h:selectOneMenu value="#{fooBean.object.value}" 
	valueChangeListener="#{fooBean.statusChanged}" 
	onchange="submit()" immediate="true">
	<f:selectItem itemLabel="" itemValue=""/>
	<f:selectItems value="#{fooBean.selectValuesList}"/>
</h:selectOneMenu>
 
Java:
public void statusChanged(ValueChangeEvent event) {
	if (event.getNewValue() != null && 
		StringUtils.hasText((String) event.getNewValue())) {
		// ... Do something with the new value
	}
}

The negative side of using onchange="submit()" is that the form is submitted, validated and you don’t get the same dynamic feeling like with a4j:support.

In JSF 2 things are easier as you don’t need the valueChangeListener and you can use the listener attribute of instead.

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