I have been doing front-end development for past 3 years and know enough node and Java to get by on server sice. I want to deepen my knowledge in backend dev in general, Java seemed like a good start because of better career prospects.
Related: Is Java still relevant? Or should I start with some other backend stack?
In terms of resources its hard to advise - different people learn differently. Some people prefer books, some youtube videos and some by example. Best bet is to google the resources
I do think Java 8 in action is an excellent book, also oracle's tutorials are good. The stackoverflow documentation pages for java are quite good too, as is dzone
For learning, you can start with reading Java Language Specification. And then you can read Java Virtual Machine Specification. After that, you should have very good understanding of big picture. Then it is just about writing code using APIs.
As for back-end, there are a lot of topics (not specific to language). File system, networking, distributed computing and others. In real production systems, it is about how to compute/process within certain time-frame. And how to operate the production systems.
https://www.udacity.com/course/intro-to-java-programming--cs...
I am curious if anyone else likes/dislikes the book.