Hibernate-extensions provides a few tools for working with hibernate-2. In particular, there are ant tasks for hbm2java, class2hbm, and ddl2hbm, as well command line utilities.
Created attachment 61183 [details] hibernate-extensions-2.1.3.ebuild This ebuild only provides the ant tasks. The console tools would require a few new packages to be made. I did some work for the console bits, including patching the build.xml.
Created attachment 61184 [details, diff] hibernate-extensions-2.1.3-console_build.patch Patch to fix console tool's build.xml.
Now maintained in the experimental overlay: https://gentooexperimental.org/svn/java/gentoo-java-experimental/dev-java/hibernate-extensions/
hibernate has been last-rited. A much newer version is alive upstream but I don't think hibernate-extensions is a thing any more.