/usr/share/java/plexus-compiler-javac-1.6.jar is in libplexus-compiler-java 1.6-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/java/../maven-repo/org/codehaus/plexus/plexus-compiler-javac/1.6/plexus-compiler-javac-1.6.jar