Hello Jim,
you can try it by doing something like this:
int number=table.getContainerDataSource().size();
//getContainerDataSourse() returns the viewing data-source container.
//.size() returns the number of visible items in the container; in your case - rows
//then ou can try by adding footer as you have done before:
table.setColumnFooter(null,String.valueOf(number))
Hopefully it will help : )