You need to be careful how you use java-runtime, because some applications explicitly depend on jre. But of course, if it's openjdk, then it surely will run with jre. Never the other way around, though, not for sure at least.
Anyway you can take a look at another java build: http://aur.archlinux.org/packages/jsampler/jsampler/PKGBUILD And yes, you have to write your own shell and desktop scripts most of the time. Download that package and take a look at those for an idea.
