From the maintainer Li Haoyi: I'm putting a 1000USD bounty on this issue, payable by bank transfer on a merged PR implementing this.

Checkstyle is a common Java linter, and we should support it as a contrib/ module to better support Java projects. We should support all common configuration options, and provide it as an CheckstyleModule to allow usage on JavaModules and ScalaModules (which can contain Java sources). This needs to come with a reasonable set of unit tests, docs, and at least one example test that can be included in the documentation

Can possibly be adapted from https://github.com/etsy/sbt-checkstyle-plugin