Depend on where you work. Most places I've worked however JPA was part of it.

Spring used to be big but today JavaEE is probably better (I've used both.)

I learned a lot from Adam Bien, he is both entertaining and he keeps it down to earth, useful and real.

Three more things:

1. Invariably someone will come to trash Java. Don't care about them. Modern Java is decent.

2. Learn an IDE. Again, someone will probably say you should learn without one and that is about as smart as saying a "good carpenter never uses power tools" i.e. batshit crazy.

Java is pretty much dependent on using tools. I can enjoy both NetBeans, Eclipse and IntelliJ. All three are better than anything you can get in any other language (except reSharper, but that is basically IntelliJ for C#)

3. Learn Maven and/or Gradle. Learn to love it. I learned to love it after that time I spent three days hunting for libraries for an older (non Java) maintenance job. Coming back to a system that will happily download and setup everything is lovely.

edit: FWIW i wrote this lar year. It is kind of indirectly related : https://erik.itland.no/questions-about-why-i-like-java