The big pain points I remember about JSP are the clunky syntax for for-loops and conditionals, and the lack of a simple way to define and use functions. A bit of Googling shows me this page from their Javadoc - https://docs.oracle.com/cd/E19879-01/819-3669/bnaio/index.ht... (you should check if that's the latest version).

I'd recommend Velocity instead. It's also quite old and stable, and takes care of the above mentioned issues - https://en.wikipedia.org/wiki/Apache_Velocity