public class BackingBean {
   ...
   public Converter getConvert() {
      return new Converter() {
         public Object getAsObject(FacesContext context, UIComponent component,
                                   String newValue) throws ConverterException { ... }
         public String getAsString(FacesContext context, UIComponent component,
                                   Object value) throws ConverterException { ... }
         };
    }
}