How to use a COMMON session attribute ??

public class SharedVariables
{

   public static Map m_mUsers = new HashMap();

  public static synchronized void addLoggedinUser(String sUser)
  {
      m_mUsers.put(sUsers, new Date());
  }

  public static synchronized void removeLoggedinUser(String sUser)
  {
       m_mUsers.remove(sUsers);
  }

}