The boundary condition

How to write the following three dimensions boundary condition in FreeFEM++?

whre J=[0,T] is the time.

This depend strongly of your formulation ans the finite element

Other wise you can make penalization.

I do not quite understand. Are there any examples available for me to learn from?

The problem dépend of your variational formulation , of your equation and of your finite element

See maxwell exemple

Where can I find the Maxwell example?