plexus-io supports java 1.5+ and has a number of jdk-level specific features. Since it requires 1.7+ to build, you can force plexus-io to use "downgrade" features even when running on 1.7, using the system property -Djava.language.downgrade=
It is therefore recommended to run mvn -Djava.language.downgrade=true clean install before relasing, to assess that features still work with older jdk versions.
PlexusIoZipFileResourceCollection removed from plexus io and added to plexus-archiver 2.10. Older versions of plexus-archiver may not be compatible with this.
In 2.1, all subclasses of AbstractPlexusIoResource now have to call appropriate parent constructor, there are no more setters.
AbstractPlexusIOResourceWithAttributes no longer exists, extend AbstractPlexusIoResource and implement interface PlexusIoResourceWithAttributes instead.