try
{
    User user = currentUser(); //Throws UnauthenticatedException if not logged in.
    //Do stuff with the user.
}
catch (UnauthenticatedException e)
{
    //Do nothing, it's perfectly fine to not do the above code
    //if the user isn't logged in.
}

currentUser.isLogged()

public void valid() throws UnauthenticatedException{
    User user = currentUser(); //Throws UnauthenticatedException if not logged in.
}

public Optional<User> authenticate(){

   User user = null;
   try {
     user = currentUser();
   }
   catch (UnauthenticatedException e){
   }

   return Optional.ofNullable(user);
}