Yeah, that's the thing: Google knew it should've paid, it looked into a license, and then decided to claim it didn't need one and go without. It's certainly not fair use, it was specifically to build a competing product/commercial ecosystem to Oracle's and they state it was fundamental to their strategy to do so.
This case has been going on since 2010. It's time Google let it go. They lost.
What Google looked into licensing was considerably broader than the APIs, and included material that everyone agrees is copyrightable.
We don't learn anything from the fact that Google negotiated for a broad licence, decided not to take one, and used a clone which copies only the API definitions.
If API definitions aren't copyrightable then Google didn't do anything wrong. If they are then it did.
The idea that API definitions may not be copyrightable certainly isn't a wild theory that Google made up for this instance.
> It's certainly not fair use, it was specifically to build a competing product/commercial ecosystem to Oracle's
The commercial nature of the work is just one factor determining fair use. Another is "the amount and substantiality of the portion used in relation to the copyrighted work as a whole". And the API structure is a quite small part of the JDK as a whole, and has a different nature than implementation code as well.
This case has been going on since 2010. It's time Google let it go. They lost.