The ebuild needs to be updated to build the packages from source
Created attachment 44743 [details] webgraph-1.4.ebuild builds webgraph-1.4 from source
Created attachment 44744 [details, diff] webgraph-gentoo.patch adds needed jar's the the classpath and add's source and target attributed to the javac node
Fixed. Available for testing as dev-java/webgraph-1.4