I have my own little openSuse build service account for the generation of same Java related packages. Mainly Groovy stuff.
If you want to use javac in the build process you need to add the build requirement to java-devel. Unfortunately this package is not available in the openSUSE_10.2 and openSUSE_10.3 standard repositories. They are available in the openSUSE_10.2:NonFree and openSUSE_10.2:NonFree repositories, but there is no option in the web interface of the build service which allows to configure this.
You have to use the build service API do change this configuration. Which is in fact very easy because the API is a REST like service which can be used for example with kwrite.
allows you do edit the configuration of the repositories. Just add
<path project="openSUSE:10.3:NonFree" repository="standard">
and you have access to the Sun Java rpms.
for more information on the openSuse build service API.