Java 9 introduces Java Platform Module System and it comes with changes to the JAR files as well. The modules are packaged into modular JAR files - a JAR file that has module-info.class file in its top-level directory. Unlike the regular JAR files, meta information such as the module version or it's main class(for the executable JAR files) are stored inside module-info.class instead of the manifest file.

A support to set the module version and main class should be added to Plexus Archiver. This feature will help tools like Maven to produce modular JAR files.