Usually a JSF page is backed by a managed bean. You request data through Expression Language (EL) expressions, like:
The managed bean would probably be called MyBean.java, though you can call it anything you want. It would have a getter method, getUnitsSold(), and in there you'd retrieve the data any way that you normally retrieve data in
Java ... read it from a file, a direct
JDBC call to a database, call to an
EJB, load it through Hibernate, etc. It's a good idea for the getter to just load data once and hold onto it for the scope of the bean, or at least the request. JSFs tend to call the getters over and over, and you don't want to keep loading the same data.