I'm using forms to do a login with a user with JSF, Glassfish and Realms linked to a database, exist some way to know the id, the username of some information to know the user logged?
I assume you mean JDBC security realm.
FacesContext context = FacesContext.getCurrentInstance();
HttpServletRequest request = (HttpServletRequest) context.getExternalContext().getRequest();
String username = request.getUserPrincipal().getName();
Then from the username, you can query the database to get any other user information you want.