I have been coding JSP's for a few years now using scriptlets and beans. What should I focus on next? JSTL, Spring or something else? Opinions, thoughts and good arguments are much appreciated.

Like other Java enterprise tools, Tomcat has migrated from the original Java EE specification to Jakarta EE. Tomcat 9 and earlier were based on Java EE; Tomcat 10 and later are based on Jakarta EE.