创建仅打印到一行的 XML

我创建了一些将映射写入 XML 的代码。它似乎可以工作，但打印的文件没有新行。所以在任何 XML 编辑器中它都只占一行。如何让它为每个孩子打印到新行？

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.newDocument();

Element vdata = doc.createElement("vouchdata");
doc.appendChild(vdata);

for (Entry<String, String> entry : vouchMap.entrySet()) {
    Element udata = doc.createElement("vouch");

    Attr vouchee = doc.createAttribute("name");
    vouchee.setValue(entry.getKey());
    udata.setAttributeNode(vouchee);

    Attr voucher = doc.createAttribute("vouchedBy");
    voucher.setValue(entry.getValue());
    udata.setAttributeNode(voucher);

    vdata.appendChild(udata);
}

// write the content into xml file
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(new File("vouchdata.xml"));

// Output to console for testing
// StreamResult result = new StreamResult(System.out);

transformer.transform(source, result);

I use

Transformer tf = TransformerFactory.newInstance().newTransformer();
tf.setOutputProperty(OutputKeys.INDENT, "yes");
tf.setOutputProperty(OutputKeys.METHOD, "xml");
tf.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");

这似乎工作得很好。