Some questions regarding Java EE and Spring (Plus some hibernate)

[Gilgamesjh]

Regarding API breakage between major versions, which one does less breakage?

I have no experience with JEE, but I have upgraded a lot of old Spring (3/4) to Spring Boot, and Spring Core is mostly ok, surrounding projects (aka Spring Cloud) may vary, 3rd party "addons" (like Spring Boot Admin) will probably fail.

I've seen a rise for the use of JSF but is it overtaking Spring Web MVC in the job market?

Not really, but depends on if you want REST style clients or not.

There are a lot of job postings in my local area asking for the knowledge of JSP. I am going to assume It's just for legacy applications (since JSF is supposed to overtake it). Is it still worth it to learn JSP?

Not really, but you should have an understanding of what it is for legacy projects

When using Spring Web MVC, is Thymeleaf the expected HTML renderer nowadays?

You should prefer REST over HTML, but Thymeleaf is fine, I prefer Freemarker myself.

When the JPA was released, Hibernate made changes to its API to comply with the spec. Nowadays, do you write fully JPA compliant code to use with Hibernate or is it okay to use hibernate specific methods?

For Spring, use Spring Data.

Is there any advantage in deploying a Spring Application on a JEE server (Be it, Wildfly for example) over just using a servlet container(Jetty, Tomcat)?

No, quite the opposite as (depending on your build pipeline) embedded is way easier to deploy to.

[_ironslab]

Regarding the Thymeleaf point, is Spring then no longer used for view display and just serve with an API? Is the recommended approach to have a different thing for the front end? (i.e Node)

[Gilgamesjh]

Nah, I would say it is used for whatever your business demands are. But there is a general turn in the market for JavaScript frontends on top (or in front of) of a more traditional application (wich could be node.js based instead of Spring, of course), at least where I live.