It is preferred to build the bytecode so that it runs on older jvms. This is done passing '-source 1.[45]' to javac (or for cdbs ant tasks setting ANT_OPTS to -Dant.build.javac.source=1.[45].
are you sure, the javac manpage only states that option affects the version the source is assumed to be for and when I tried adding that option to the build for libgdata-java it didn't seem to make any difference to the class file version generated