Not Java. JVM. Many often confuse them. People dislike Java (not without merits), and because of that, they'd naturally dismiss JVM as a viable technological choice. JVM, as a matter of fact, is a pretty cool piece of technology. Learning the fundamentals of JVM and its internals is a good career investment without a doubt. And you don't really need to be a Java expert to build things to run on JVM.

Do you have any good link/books for learning about JVM?

I found that there are tons of beginner java, but nothing on JVM.

I've only found by Scott Oaks Java Performance, which gives some interesting knowledge about JVM but it's a secondary focus.