I have installed dev-java/icedtea6-1.6.2-r1 from the java-overlay with USE="doc examples javascript nio2 nsplugin xrender -cacao -debug -pulseaudio -systemtap -zero". Several files of the API documentation link to the technotes/ directory. For an example, see <URL:file:///usr/share/doc/icedtea6-1.6.2-r1/html/api/java/security/KeyFactory.html#getInstance%28java.lang.String%29> (link to “Java Cryptography Architecture API Specification & Reference”). The technotes are not installed with icedtea6, so some links are broken. Workaround (if an Internet connection is available): read the documents online: http://java.sun.com/javase/6/docs/technotes/…
Well we install everything the package builds. The technotes just are not there. You can get them via dev-java/java-sdk-docs but that is fetch restricted package and we wouldn't want to make that a dependency of icedtea. So unless you can find a free alternative... sorry.