Despite Mustache templates are popular especially on the client side it's possible to use it on the server side as well. And benefits? It has simple yet powerful syntax. It's performant and alo resistant to bad practices such as complicated JSP scriptlets. It's also universal, i.e. you could use it to render any text documents (web pages, e-mails, etc.).
Java developers mostly know JSP, Velocity, Freemarker and JSF Facelets. These tools are feature-rich, mature and proven. Still they're not perfect (actually nothing is). So if none of those "proven" tools fits your needs without tradeoffs try Trimou!
Trimou is an open source Mustache implementation focused on extensibility and configurability. There are some useful built-in extensions: CDI, Servlet, PrettyTime, Minify and google-gson. It also has a decent test coverage and documentation. Since 1.5.0 Trimou defines a helper API inspired by Handlebars project.
See also the project site: http://trimou.org/
Don't forget to check the example web application!