Concepts (open for discussion)

Requirements

Maven >= 3.3.1
Java >= 8

General

All modules should use only one primary build system
It should be super-easy for new contributors to get started (A new contributor should be able to checkout and build with a core testsuite with a simple: 'mvn package' run)
New code should only be accepted, if there are tests (Currently the java part of the build is configured to fail if the code coverage is below 90%)

Java Specific

Development should be done in Java >=9
Providing Java 7 compatible versions should be possible by using the retrolambda plugin
- Usage of default implementations does cause more problems than it solves in this case.

IDE specific

For formatting there is a .editorconfig defined. Intellij Idea come with a plugin for this pre-installed, for eclipse an installation is required (http://editorconfig.org/).
Import organizing uses the Intellij Idea default:
- Import order
  - all other imports
  - blank
  - import javax.*
  - import java.*
  - blank
  - all other static imports
- Star imports
  - number of imports needed for .* = 5
  - number of static-imports needed for .* = 3