 <p>From the documentation:</p> <pre> You can also explicitly control the exact type of Map that will be instantiated and populated via the use of the 'map-class' attribute on the element. </pre> <p>So, for example, you can take <code>DefaultedMap</code> from <code>commons-collections</code> and try to use it as <code>map-class</code>. Or you can implement your own <code>Map</code> and use it.</p>