Dynamically red negative numbers in report - jasper-reports

Question

All negative numbers in my report will need to be red. Is there any way I can do this through the number formatting? If not, is it possible to create a dynamic conditional somewhere that would check the current text field?
for example:
If this Textfield < 0 then this texfield font is red
Keep in mind, it would need to be dynamic in the sense that I could drop it on all the textfields without changing the condition.
I do understand conditional styles, however rather than using specific fields for the condition (as in the question this is marked for duplicate against) I'd like to allow the condition to be dragged onto any text field and distinguish whether or not it is less than 0.

Answer 1

You cannot achieve this with conditional styles.
The solution would be to create a custom formatter that would output styled text and have the textField configured with markup="styled" like so:
<textField>
<reportElement x="72" y="16" width="100" height="24" uuid="698866c8-7d26-4bc7-8727-b4a56d239a53"/>
<textElement markup="styled"/>
<textFieldExpression><![CDATA[NegativeNumberFormatter.format($F{A1}, "#,##0.###")]]></textFieldExpression>
</textField>
NegativeNumberFormatter might look like this(using default package):
import java.text.DecimalFormat;
public class NegativeNumberFormatter {
public static String format(Number n, String pattern) {
if (n != null) {
if (n.doubleValue() < 0) {
DecimalFormat df = new DecimalFormat();
if (pattern != null) {
df.applyPattern(pattern);
}
return "<font color=\"red\">" + df.format(n) + "</font>";
} else {
return "" + n;
}
}
return null;
}
}