1.6 is the only supported JAVA for CPO 2.1 through 2.3.X and is required. JAVA 1.7 will be required and supported with CPO 3.0 which should release in the next couple of weeks. I believe slated for end of this month.
You *cannot* use 1.7 with anything other than CPO 3.0 or many of the adapters and functions will not work because there was some major differences between 1.6 and 1.7 (from what I've heard).
CIAC Adoption Pilot Engineering Lead