Anyway, i think we have to have a stance on this whether we will support or not Java 7 and forums announcement is not enough. If we go with Java 8 for Debian, we should probably put "(Java 8+)" or something near the download link.
Hit this today on Debian Jessie, very annoying. I downgraded to 4.0.1 to avoid this, as I have some other reasons to avoid 1.8 for now.
Based on the provided workaround, I've prepared this fix: https://github.com/igniterealtime/Openfire/pull/626
This should allow Openfire to be build with Java 8, while not causing issues when executed by Java 7.
Note that a similar change needs to go in the Master branch. My PR is against the 4.0 branch.
The fix has now been applied to the 4.0 branch as well as to master.