How to get the current from current density

Hi Everyone,
I am simulating a piezo electric transducer in COMSOL Multiphysics 4.0a. In order to get the impedance of the transducer at different frequencies, I need the current flowing at the boundary of piezo ceramic. My model is 2D axisymmetric. Following are my problems:

1. For getting current(I) from the variable current density(J), I have to integrate the expression:
int(J*2*pi*r)dr over the boundary
However, I came to know from my friend that multiplication by (2 *pi *r) is applicable for COMSOL 3.5 but COMSOL 4.0a does this automatically through internal calculations for axisymmetric models. So there is no need to evaluate int(J*2*pi*r)dr. Rather int(J)dr is appropriate. Please confirm if it is correct.

2. How can I get the integration of current density. Using probe option, model coupling etc. Expedite if anyone have an idea

3. If I get the current by above means, then how to plot this impedance (Z=V/I), versus frequency. I mean how to access current value and corresponding frequencies to plot line graph.

Hope to hear anyone soon, Thanking you in anticipation
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User COMSOL