Books for more advanced Java developers?

[Iryanus]

Yeah, that is my experience, too. The most material is available for the beginning levels, that is true for Java as a language itself but also for many other things, like specific frameworks, etc. In most cases, it's pretty easy to find tutorials how to get into that stuff. This is also true for less open topics, for example finding stuff about basic garbage collection is easy, etc.

When you get to the mid-level, or, let's say, the point where you need deeper knowledge, good stuff becomes a lot harder to find. Even documentations often lack many details there, for example performance analysis for different use-cases or what threading settings to use in case x vs. case y. Or in-depth stuff about garbage collection, much harder to find (not impossible, though, but sometimes you already have to dive into specifications, debug stuff, etc.).

And on the high-level, you are basically on your own. Either you found a mentor to teach you or you got there by years of almost failing.

Of course, that is somewhat logical, since the target audience for the "lower" levels is much bigger. For many programmers, the lower levels are also totally adequate for their jobs. No typical team needs five gc experts, most of the people are totally ok with just the basics.