Ask HN: How to learn Java EE?

I am a programmer for ~15 years, currently freelancing. Know Java SE, PHP MVC frameworks, Fortran, Swift etc. I'd like to learn Java EE since this is where the most profitable gigs are (and probably will be for some time). However, to me the environment looks complex as it evolved over many years, so I don't know where to start. Any tips for useful resources on how to get into the current state of the art? Ideally, a single book :-)