HashMap< String, ArrayList<String> >: Unable to populate the Array List from JSP

hi,

When we had the data structure as: HashMap<String,String> the following jsp fragment was able to populate it:
<s:textfield name="map['key']" />

but the same thing is not working with HashMap<String, ArrayList<Stirng> > when we tried:
<s:textfield name="mapOfList['key']".

We also tried instantiating the object in the action class constructor:
mapOfList = new HashMap<... >();
mapOfList.put("key", new ArrayList());

still no luck.... Using POJOs instead of hashmap would not fit to my requirements.

any help ???

cheers,
ravi