1. namespaces "c" and "fn" should be declared:
xmlns:c="http://java.sun.com/jsp/jstl/core"
xmlns:fn="http://java.sun.com/jsp/jstl/functions"
2. Create an String array by splitting the request uri, using „/“ as delimiter. Use the first array element as value for the “myString” variable.
<c:set var="myString" value="${fn:split(requestScope['javax.servlet.forward.request_uri'],'/')[1]}"></c:set>