Maven and Java multi-version modules

Introduction Usually, a project has a minimum Java version requirement and that applies to all of its modules. But every rule has its exceptions, as recently I stumbled on the following issue. One open source project of mine mandates Java 1.6 for most of its modules, except one requiring the 1.7 version. This happens when integrating external libraries having different Java requirements than your own project. Because that one module integrates the DBCP2 framework (supporting at least Java 1.7), I need to instruct Maven to use two different Java compilers.