Thanks a lot for looking into this for me.
it's exactly same as example i am trying to test foud at
http://java.boot.by/wcd-guide/ch07s04.html only thing different in mine is that MyELFunctions class is inside classes directory instead of package.
<%@ taglib prefix="my" uri="http://www.server.com/example-taglib" %>
<html>
<head><title>EL Function example</title></head>
<body>
str1 is : ${param["str1"]} <br>
str2 is : ${param["str2"]} <br>
concatenated : ${my:concat(param["str1"], param["str2"])}
</body>
</html>