Is there some public gentoo repository for installing java-related stuff? Could be layman or whatever.
Things I'm interested in are: apache-activemq, apache-solr, fusesource etc.
The layman repository java contains a lot of java packages, but fuse is the only one in your list that can be found there.
I suggest you take a look at http://gpo.zugaina.org/. There you can search for ebuilds and a lot of overlays are included.