As of August 7th, 2016 the docs have recommended against using OpenJDK.
A famous alternative to Oracle Java is the OpenJDK. Note that openHAB may be unstable and slower executed by OpenJDK, it is therefor recommended to switch to Oracle Java if possible.
The current docs state:
OpenJDK may also be used, but it has some known limitations with openHAB and is not recommended.
I have a vague recollection that this warning was also in place on the old openHAB 1.x wiki.
@mstormi, given that this warning has been in place for at least three years, maybe it’s worth removing it from openHABian now? I’m a little surprised that openHABian bothers to install it by default.