This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Your JVM is apparently running under a spanish locale. The simple number (and date) formatting services have picked the notation appropriate for that locale, which would be "123.456.789,00" instead of the English "123,456,789.00" format. It could be worse. I think in Peru, it's more like "1234'5678'9000" and I don't recall if they use "," or "." for the decimal point.
Your options are as follows. Pick one:
1. Override the default locale for the JVM
2. Override the locale setting on the converter by including an explicit locale attribute.