Learning java as a self thaught programmer

I am a mostly self taught programmer. I've been programming for past 3 years professionally but the problem is that still most of my work is done by googling and trial&error. While I learn a lot I feel kinda guilty being paid for this. Since I work mostly with java I decided to really master it. What course would be the best to really LEARN java. (java programming patterns, how to properly do try/catch/finally, when to create a class, when to inherit it...) after that I'd like to master java spring boot.

So what I am looking for is how to build good foundation knowledge, so I don't feel like a fraud when talking with someone who knows his stuff... for example I still have problems with java servlets, streams etc.. even though I've been working with them for past 2 years.