Originally Posted by
CPH-Flyer
In the Schengen area customs clearance takes place at the final destination. You will just need to go through passport control in Barcelona.
In my own experience, checked bags clear customs when they are transferred from non Schengen to Schengen (without you needing to picking them and clear custom the same way you have to do in USA) and there’s no custom check at your final destination. Otherwise how would it work if your final destination is a domestic only airport?