Even for strict java builds, I've been using 'sbt' (the Scala Build Tool). It really is the successor to gradle, in many regards. Not sure you've tried it as one of your alternatives, but I'd implore you to give it a try.
Also the plugin ecosystem is not as wide as Gradle and SBT lacks a daemon, which makes builds 3X/4X faster in Gradle.
For Java builds (especially multi-modules builds) I still prefer Gradle.