Updating xml and saving it removes namespace prefix of the root element and all nodes

Question

I am loading a xml and updating some value and then again saving the back. In this scenario the namespace prefix of the root element and all nodes is getting omitted.

I am working with Java version: JDK-17

There is no error in generating the output.

Input xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> 
<foo:Config xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:foo="http://cc.bb.aa/def"> <foo:isEnabled >false</foo:isEnabled> </foo:Config>

output

<?xml version="1.0" encoding="UTF-8"?>
<Config xmlns:foo="http://cc.bb.aa/def" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<isEnabled>true</isEnabled>
</Config>

supporting code

public class UpdateElem {

    public static void saveDocToFile(final Document doc, final Path file) {
        try {
            Transformer transformer = TransformerFactory.newInstance().newTransformer(new StreamSource(new StringReader((
                  "<xsl:stylesheet version=\"1.0\" xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">\n"
                + "    <xsl:output method=\"xml\" indent=\"yes\" encoding=\"UTF-8\"/>\n"
                + "    <xsl:strip-space elements=\"*\"/>\n"
                + "\n"
                + "    <xsl:template match=\"@*|node()\">\n"
                + "        <xsl:copy>\n"
                + "            <xsl:apply-templates select=\"@*|node()\"/>\n"
                + "        </xsl:copy>\n"
                + "    </xsl:template>\n"
                + "\n"
                + "</xsl:stylesheet>"
            ))));
            // handle DOCTYPE setting
            if (doc.getDoctype() != null) {
                String systemValue = doc.getDoctype().getSystemId();
                transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, systemValue);
            }
            transformer.transform(new DOMSource(doc), new StreamResult(file.toFile()));
        } catch (TransformerFactoryConfigurationError | TransformerException e) {
            e.printStackTrace();
        }
    }
    
    public static Document getDocument(final Path file) {
        final DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = null;
        Document doc = null;
        try {
            docBuilder = docBuilderFactory.newDocumentBuilder();
            doc = docBuilder.parse(file.toFile());
        } catch (Exception e) {
            e.printStackTrace();
        }
        return doc;
    }

    public static void main(String[] args) {
        Path xml = Paths.get("user.xml").normalize();
        Document doc = getDocument(xml);
        NodeList sslConfig = doc.getElementsByTagName("foo:Config");
        System.out.println("sslConfig= "+sslConfig);
        Element sslConfigElement = (Element) sslConfig.item(0);
        NodeList nodeList = sslConfigElement.getElementsByTagName("foo:isEnabled");
        if ("true" != null && !nodeList.item(0).getTextContent().equals("true")) {
            nodeList.item(0).setTextContent("true");
        }
        try {
            saveDocToFile(doc, xml);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }```

Michael Kay · Accepted Answer · 2025-07-02 20:12:22Z

1

Try setting the DocumentBuilderFactory to be namespace-aware.

docBuilderFactory.setNamespaceAware(true)

(Also, there's no point building a DOM just for the sake of transforming it. Most XSLT processors will build a more efficient tree if you give them a SAXSource or StreamSource.)

answered Jul 2 at 20:12

Michael Kay

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2 Comments

TheUser Jul 3 at 5:08

thanks @Michael, this solution works but when i try to find an element it fails.

final XPath xpath = XPathFactory.newInstance().newXPath(); Node result = (Node) xpath.compile("/foo:Config/foo:isEnabled").evaluate(doc, XPathConstants.NODE); 		System.out.println(result);

This returns null

Michael Kay Jul 4 at 7:05

If you use namespace prefixes in an XPath expression then you need to declare them, using xpath.setNamespaceContext().

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