Dual zipfs

[bitozoid]

I'm running icedtea jre on gentoo.

/opt/icedtea-bin-7.2.6.6/jre/lib/rt.jar contains "java.util.zip" package.

/opt/icedtea-bin-7.2.6.6/jre/lib/ext/zipfs.jar contains
"com.sun.nio.zipfs" package.

1) Why both packages exist? They look quite similar.

2) Where are the sources for the latter?

Thanks in advance.