Portlets inheriting from UIPortelet constructor parameters?

["FLORENT.TROLAT" <FLORENT.TROLAT@xxxxxxxx>]

I would know where the constructors of portlet inheriting from  
UIPorlet  can be found or configured :
public class UIOrganizationPortlet extends UIPortlet {

public UIOrganizationPortlet(UIGroupNode uiGroupNode,
                             UIMembershipNode uiMembershipNode) throws 
Exception {
  setId("organization-portlet");
...

In this example where in eXo the params UIGroupNode uiGroupNode, 
UIMembershipNode uiMembershipNode are passed to the portlet (xml file? 
java hook?).

Thank you for your help
flo.