<h:form>
 <rich:panelBar height="400" width="500" valueChangeListener="#{userBean.valueChanged}">
 <a4j:support event="onitemchange"></a4j:support>
 <rich:panelBarItem
 label="Leverage the whole set of JSF benefits while working with AJAX">
 Ajax4jsf is fully integrated into the JSF lifecycle. While other frameworks only
 give you access to the managed bean facility, Ajax4jsf advantages the action and value
 change listeners as well as invokes server-side validators and converters during the
 AJAX request-response cycle.
 </rich:panelBarItem>
 <rich:panelBarItem
 label="Add AJAX capability to existing JSF applications">
 The framework is implemented using a component library. The library set Ajax
 functionality into existing pages, so there is no need to write any JavaScript
 code or to replace existing components with new Ajax one. Ajax4jsf enables page-wide
 Ajax support instead of the traditional component-wide support and it gives the
 opportunity to define the event on the page. An event invokes an Ajax request and areas
 of the page which are synchronized with the JSF Component Tree after changing the data
 on the server by Ajax request in accordance with events fired on the client.
 </rich:panelBarItem>
 <rich:panelBarItem
 label="Write your own custom rich components with built-in AJAX support">
 Component Development Kit (CDK) is a design-time extension for Ajax4jsf. The CDK includes
 a code-generation facility and a templating facility using a JSP-like syntax. These
 capabilities help to avoid a routine process of a component creation. The component
 factory works like a well-oiled machine allowing the creation of first-class rich
 components with built-in Ajax functionality even more easily than the creation of
 simpler components by means of the traditional coding approach.
 </rich:panelBarItem>
 <rich:panelBarItem
 label="Package resources with the application's Java classes ">
 In addition to its core, Ajax functionality of Ajax4jsf provides an advanced
 support for the different resources management: pictures, JavaScript code, and
 CSS stylesheets. The resource framework makes possible to pack easily these
 resources into Jar files along with the code of your custom components.
 </rich:panelBarItem>
 <rich:panelBarItem label="Easily generate images on-the-fly">
 Resource framework can generate images on-the-fly so that it becomes possible
 to create images using the familiar approach of the Java graphic2D library.
 </rich:panelBarItem>
 <rich:panelBarItem
 label="Create a modern rich user interface look-and-feel with skins-based technology">
 Ajax4jsf provides a skinnability feature that allows easily define and manage
 different color schemes and other parameters of the UI with the help of named
 skin parameters. Hence it is possible to access the skin parameters from JSP
 code and the Java code (e.g. to adjust generated on-the-fly images based on
 the text parts of the UI). Note: skinnability is not an equivalent of traditional
 CSS, but a complement.
 </rich:panelBarItem>
 <rich:panelBarItem
 label="Test the components, actions, listeners, and pages as you are creating them">
 An automated testing facility is in our roadmap for the near future. This facility
 will generate test cases for your component as soon as you develop it. The testing
 framework will not just test the components, but also any other server-side or
 client-side functionality including JavaScript code. What is more, it will do all
 of this without deploying the test application into the Servlet container.
 </rich:panelBarItem>
 </rich:panelBar>
</h:form>

public void valueChanged(ValueChangeEvent event) {
 System.out.println("UserBean.valueChanged()");
 System.out.println(event.getNewValue());
 }

just rerender the components you need after some activities in listener.

I successfully used a code
like the following :

<rich:panelBarItem name="aPanelBarItem" label="aPanelBarItem" >
 <a4j:support event="onenter" reRender="aPanelBarItemContent"
 action="#{myBean.loadContent}"/>
 <h:panelgroup id="aPanelBarItemContent">...