How to correct/center GridLayout using standard Java layout managers?

Question

The below code represents the problem. Since I have heights of the north and south panels set the rest of it goes to the center panel using GridLayout. I think that since it

Answer 1

How to make sure that when the GridLayout is not taking the whole space it is at least centered?

JPanel wrapper = new JPanel( new GridBagLayout() );
wrapper.add( centerP );
contentPane.add(wrapper, BorderLayout.CENTER);  
//contentPane.add(centerP, BorderLayout.CENTER);