Java programs are difficult to build. Tex has even put pre-built java binaries in a few packages. The problem as I understand it is that java programmers don't all use the same build tools. They don't usually worry about making it easier for packagers, because the binaries work on multi-platforms. Ideally, the actual compiling instructions should be in the spec file, but unless you have a working spec file to start with it's not easy.
Galen