ADF : Groovy: How to use Groovy Expression for ViewObject -> BindVariable

--------------------------------------In My VOImpl-------------------------------------------------------

import oracle.apps.fnd.applcore.common.ApplSessionUtil;

public String getLoggedInUser(){
String loggedInuser = "";
if(ApplSessionUtil != null){
loggedInuser = ApplSessionUtil.getUserName();
}
return loggedInuser;
}
----------------------------------In VO.xml -> For Bind Variable -> Expression-------------------------

adf.object.viewObject.loggedInUser