We use CGLIB to enhance a half-baked Java Bean with no firePropertyChange() invocations in its setters, into a bean that does fire PropertyChangeEvent's from its setters.

Code Snippet

Our QBeanInterceptor registers the PropertyDescriptor's setters methods into a setterMap.

public class QBeanInterceptor extends QInterceptor {
    BeanInfo beanInfo;
    Map<Method, PropertyDescriptor> setterMap = new HashMap();
    BeanPropertySupport beanAnnotation;
    boolean fireByDefault;
    ...
    public Object invoke(Object target, Method method, Object[] args,
            MethodProxy proxy) throws Throwable {
        Object oldValue = null;
        Object newValue = null;
        PropertyDescriptor propertyDescriptor = null;
        if (args.length == 1 && fireAtWill(method)) {
            newValue = args[0];
            propertyDescriptor = setterMap.get(method);
            if (propertyDescriptor != null) {
                oldValue = getOldValue(target, propertyDescriptor);
            }
        }
        Object result = super.invoke(target, method, args, proxy);
        if (propertyDescriptor != null) {
            QBean bean = (QBean) target;
            bean.getPropertyChangeSupport().firePropertyChange(
                    propertyDescriptor.getName(), oldValue, newValue);
        }
        return result;
    }
    ...
}    

where if the method is a key to an associated PropertyDescriptor in setterMap, then we invoke firePropertyChange() to fire a PropertyChangeEvent.

Demo

Here is a trivial demo that is hardly worth downloading. And it's quite large, because it depends on a CGLIB jar.

  (BeanAspectDemo, 250k/850k, unsandboxed, Java6)