JSTL/JSP EL (Expression Language) in a non JSP (standalone) context

You can just use the Universal Expression Language itself. You need an implementation (but there are a few to choose from). After that, you need to implement three classes: ELResolver, FunctionMapper and VariableMapper.

This blog post describes how to do it: Java: using EL outside J2EE.

StringTemplate is a more lightweight alternative to Velocity and Freemarker.

I would recommend looking into Apache Velocity. It is quite simple and lightweight.

We are currently using it for our e-mail templates, and it works very well.

You can use Casper very similar to jsp and easy to use : Casper