A320 Captain reported the First Officer was locked inside the lavatory for 10 minutes but was able to eventually get out and return to the cockpit.

Narrative

FO got locked out on lav door for 10 minutes. I called Dispatch and when [we] were going to get transfer with Maintenance Control; the FA called me that the FO was out back to cockpit.My plan of action was to use a deadheading CA Airbus pilot to assist me in case if I had to call ATC for emergency. In this case FO we got him out in time. No need to call emergency in that moment.