findByUsername or find method of Facade absract class

I'm trying to make a Login app with JSF, and I found in forums that a lot of people use LoginByUsername(or findByUsername or whatever they call it ,anyway a method that does find the username and returns the user) and they put it in the facade(session bean for entity class) ! But the facade itself gives us something called find(Object id) ,and the id is username . so what's better? and why?

thanks in advance for your help