Struts help--how to use other than String, vector in a bean?

[SpaceAgeJuliet]

I am using Struts, and JSTL at the moment, but am a beginner.
I can get values in and out fine that are strings, string arrays and
vectors in my beans.
normally i just declare string or vector value in bean, with getters
and setters, and struts populate knows how to store correctly when a
form is submitted.

But, I would like to use a TreeMap in a bean, too.

Can anyone tell me how to do this? I made a treemap into my bean, with
getters and setters, and I tried to store it like this in my jsp:

....
<c:when test="${UserAccessBean.portfolioAccess[groupLoop.count-1] eq
'Read Only'}">
<select name="test">
<option key="<cut value="${group}"/>" value="No Privilege">No
Privilege
<option key="<cut value="${group}"/>" value="Read Only" <c:if
test="${UserAccessBean.updateCurrentPortfolioAccess2[groupLoop.count-1]
eq 'Read Only'}"> <cut value="selected" /> </c:if> >Read Only
</select>
</c:when>
....


Any help appreciated!

The form displays right but when i make selection and click submit, I
got:

java.lang.IllegalArgumentException: argument type mismatch