investigate moving from tomcat (Servlet API) to a full J2EE environment, such as WebSphere liberty.
the reason is so that some dependencies such as jax-rs can be used without having to manage them as manual jar dependencies. We may even be able to simplify or reduce some of the existing dependencies, and it would be fewer libraries to keep up to date. jax-rs in particular would allow improved RESTful APIs rather than the homegrown stuff we are using now.
The complexity delta for developers is actually pretty small- instead of "click tomcat, download, install" it is "click Liberty, download, install". Instead of "Run on server.. Tomcat" it is "Run on server.. Liberty".