JSTL, XPath and the State Tag Library
One of the projects I'm working on has a requirement to assign a user's permissions by state. I'm using the state tag library, which makes it very easy to make a drop-down of states. So, rather than creating a "states" table in the database, I wanted the ability to lookup state's abbreviations and full names in the tag library (since only abbreviations are stored in the database, as a comma-delimited list). So I used JSTL's XML tag to capture the output of this tag and then filter the states with XPath for the user's assigned states. Pretty slick IMO.
<label>Viewable States</label>
<%-- Sets the available states so they can be parsed with XPath --%>
<c:set var="statesHTML">
<state:state name="state"/>
</c:set>
<%
// fake it for demo - real version has these as a bean property
String[] states = {"CO", "AZ"};
pageContext.setAttribute("userStates", states);
%>
<x:parse var="states" xml="${statesHTML}"/>
<%-- Loop through and parse the list of states --%>
<x:forEach var="option" select="$states/select/option">
<c:forEach var="current" items="${userStates}"
varStatus="status" >
<x:if select="$option/@value[. = $current]">
<x:out select="$option/text()"/>
<c:if test="${!status.last}">,</c:if>
</x:if>
</c:forEach>
</x:forEach>