Add the plugin to
addSbtPlugin("com.lightbend.sbt" % "sbt-java-formatter" % "0.4.3")
This plugin uses the Google Java Format library, which makes it quite opinionated and not particularly configurable.
If you want to tweak the format, take a minute to consider whether it is really worth it, and have a look at the motivations in the Google Java Style Guide. If you decide you really need more flexibility, you could consider other plugins such as the sbt-checkstyle-plugin
Yes, we'll happily accept PRs to improve the plugin, but please note that the plugin is very rough around the edges.
Take a look at the contributors graph if you want to contact any of the contributors directly.