Welcome to the JavaRanch, Trip!
What you really need is something that validates
before conversion is attempted. Your problem is that convertNumber is using the stock
Java numeric construct/convert methods, which tend to ignore the non-numeric stuff. You probably cannot use the "pattern" attribute - I think that it only applies to the number part of the input.
I was thinking that there was a regular-expression validator that could be used, but I couldn't find it in the JSF 1.x docs. It is definitely available in JSF2, though.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.