src/test/java/freemarker/manual/UnitAwareTemplateNumberFormatFactory.java

package freemarker.manual;

import java.util.Locale;

import freemarker.core.Environment;
import freemarker.core.TemplateNumberFormat;
import freemarker.core.TemplateNumberFormatFactory;
import freemarker.core.TemplateValueFormatException;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateNumberModel;

/**
 * A number format that takes any other number format as parameter (specified as a string, as
 * usual in FreeMarker), then if the model is a {@link UnitAwareTemplateNumberModel}, it  shows
 * the unit after the number formatted with the other format, otherwise it just shows the formatted
 * number without unit.
 */
public class UnitAwareTemplateNumberFormatFactory extends TemplateNumberFormatFactory {

    public static final UnitAwareTemplateNumberFormatFactory INSTANCE
            = new UnitAwareTemplateNumberFormatFactory();

    private UnitAwareTemplateNumberFormatFactory() {
        // Defined to decrease visibility
    }

    @Override
    public TemplateNumberFormat get(String params, Locale locale, Environment env)
            throws TemplateValueFormatException {
        return new UnitAwareNumberFormat(env.getTemplateNumberFormat(params, locale));
    }

    private static class UnitAwareNumberFormat extends TemplateNumberFormat {

        private final TemplateNumberFormat innerFormat;

        private UnitAwareNumberFormat(TemplateNumberFormat innerFormat) {
            this.innerFormat = innerFormat;
        }

        @Override
        public String formatToPlainText(TemplateNumberModel numberModel)
                throws TemplateModelException, TemplateValueFormatException {
            String innerResult = innerFormat.formatToPlainText(numberModel);
            return numberModel instanceof UnitAwareTemplateNumberModel
                    ? innerResult + " " + ((UnitAwareTemplateNumberModel) numberModel).getUnit()
                    : innerResult;
        }

        @Override
        public boolean isLocaleBound() {
            return innerFormat.isLocaleBound();
        }

        @Override
        public String getDescription() {
            return "unit-aware " + innerFormat.getDescription();
        }

    }

}