DecimalFormat, SimpleDateFormat - Threading Issues

The classes java.text.DecimalFormat and java.text.SimpleDateFormat are very useful, but Sun's implementation is not thread-safe. It means that if you want to have a static instance of any of these classes in your EJB, Servlet or JSP page, you can have sporadic problems with incorrect formatting.
You'll need to use a ThreadLocal, or use a local object.
ThreadLocal sample usage:

private static ThreadLocal defaultCurrencyFormat  = new ThreadLocal() {
    protected synchronized Format initialValue() {
        return new DecimalFormat ("0.00",
            new DecimalFormatSymbols (new Locale ("pt", "BR")));
    }
};

...

String s = defaultCurrencyFormat.get().format (123.45);

You'll need to use an additional "get".