import com.liferay.portal.util.PortalUtil;
import com.liferay.portal.model.Layout;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

ByteArrayOutputStream b = new ByteArrayOutputStream();
ObjectOutputStream o = new ObjectOutputStream(b);

Object previousLayout =   PortalUtil.getHttpServletRequest(actionRequest).getSession().getAttribute("PREVIOUS_LAYOUT");

o.writeObject(previousLayout);

if (previousLayout !=null) {
 out.println("Previous Layout session object size:" + b.toByteArray().length);
}