Would it be possible to do one of the following,
1. Add an attribute to text-fields that marks a particular value as something that should be formatted in the output rather than in jasper? This would allow us to do what I'm achieving here without using the Map.
2. Allow "magic" tokens to be specified in the pattern attribute which tell Jasper to do do any formatting on the value but simply pass it through to the report (one could then create mappings which explicitly mapped those magic tokens to various formats without having to ensure they use a) a valid java format and b) a format that always returns data in the right precision for their application).