I think Java would be a better second language than Ruby. It is radically different from JS despite the name and is incredibly useful to know due to its wide usage. It also serves as one or the lingua francas of the CS community (alongside C of course).
Not that I think Java is a pleasant language. It is quite a monstrosity in terms of syntax and verbosity, but that doesn't mean it isn't useful to know.
As a data point, I started actual-programming in Perl 15 years ago, started on Rails about 10 years ago, and am now taking Java classes to get some interview-question fundamentals under my belt, since Rails is historically a recovery path for Java programmers. I don't know how it works the other way around, but for me Java has been pretty easy after writing Ruby for some years.
And you're coming into java at a better time - lambdas and inferred generic types for contractor calls reduce the boiler plate a little.
I work on a big java project - I'd love to write new stuff in kotlin though.
It's really interesting to be going in the other direction. People learn Java/C++ in university, then get jobs writing PHP or whatever. I can't imagine how cynical that would make a person, at the very least against their student loans! Not to language-war, natch. But going "in reverse" really feels like an excavation. "Interesting, this is what they had (have, like in your case) to do before langs/frameworks evolved!"
Not that I think Java is a pleasant language. It is quite a monstrosity in terms of syntax and verbosity, but that doesn't mean it isn't useful to know.