Here is an example of using JDOM to create a new XML file:

// require(groupId:'xmlunit', artifactId:'xmlunit', version:'1.0')
// require(groupId:'jdom', artifactId:'jdom', version:'1.0')
import javax.xml.parsers.DocumentBuilderFactory
import org.custommonkey.xmlunit.*
import org.jdom.output.XMLOutputter
import org.jdom.*

def addCar(root, name, make, year, country, type, text) {
    def car = new Element('car')
    car.setAttribute('name', name)
    car.setAttribute('make', make)
    car.setAttribute('year', year)
    root.addContent(car)
    def countryNode = new Element('country').setText(country)
    car.addContent(countryNode)
    def record = new Element('record').setText(text)
    record.setAttribute('type', type)
    car.addContent(record)
}

def root     = new Element('records')
def document = new Document(root)
document.setRootElement(root)

addCar(root, 'HSV Maloo', 'Holden', '2006', 'Australia',
        'speed', 'Production Pickup Truck with speed of 271kph')
addCar(root, 'P50', 'Peel', '1962', 'Isle of Man',
        'size', 'Smallest Street-Legal Car at 99cm wide and 59 kg in weight')
addCar(root, 'Royale', 'Bugatti', '1931', 'France',
        'price', 'Most Valuable Car at $15 million')

// convert resulting document to a string so that we can compare
XMLUnit.setIgnoreWhitespace(true)
def writer = new StringWriter()
new XMLOutputter().output(document, writer)
def xmlDiff = new Diff(writer.toString(), XmlExamples.CAR_RECORDS)
assert xmlDiff.similar()

We have used XMLUnit to compare the XML we created with our sample XML. To do this, make sure the sample XML is available, i.e. that the following class is added to your CLASSPATH:

You may also want to see Using MarkupBuilder for Agile XML creation.