Liferay uses Velocity templates not only to design a theme, also to reference objects defined in Java  code.

Velocity is a Java-based template engine.  As we use Velocity for web development, web designers can work in parallel with Java programmers to develop web sites according to the Model-View-Controller (MVC) model. That means that web page designers can focus wholly on creating a site with an awesome, and programmers can focus solely on writing code.
Velocity separates Java code from the web pages, making the web site more maintainable over its lifespan and providing a viable alternative to Java Server Pages (JSPs) or PHP .

But Velocity’s capabilities reach well beyond the realm of the web; for example, it can be used to generate SQL, PostScript and XML from templates. It can be used either as a standalone utility for generating source code and reports, or as an integrated component of other systems. For instance, Velocity provides template services for the Turbine web application framework, together resulting in a view engine facilitating development of web applications according to a true MVC model.

Here are some links:
Apache Velocity Project
Velocity on the Wikipedia