Looking for Java books/courses covering modern approaches?

Question

Java

As far as I know, the language is used and developed today in server technologies, and has several ways of multi-threaded programming (I may be wrong, there may be several libraries in one way, I am now a JS full stack programmer with a year and a half experience)
Recommend books on Java without water for novice programmers, books about using the language specifically for the back-end and also on multithreading and reactive programming (as far as I know, there is an Rx implementation on top of Java threads).

Answer 1

Your question title is very different from the text. You see, over the past 15 years, nothing has fundamentally changed in Java, either in terms of multithreading or in terms of web development. For the former, Brian Goetz's "Java Concurrency in Practice" remains the best textbook. For the second, there are no primers. In Java, web programming = enterprise programming, and it is considered that there is nothing to go into the enterprise until you are proficient in Java Core. Yes, and existing tutorials will mostly cover classic topics - Java EE standards, Hibernate, Spring Core, Spring MVC and Spring Data. You will have to study modern approaches, like Spring WebFlux, according to the documentation.
Separately, I would like to mention the primer of Long and Bastani "Java in the cloud", which seems to be about modern approaches to web development in Java, but in fact a dull advertising booklet.