apache/maven · error · XmlReaderException

Invalid namespace '" + model.getNamespaceUri() + "' for mode

Error message

Invalid namespace '" + model.getNamespaceUri() + "' for model version " + model.getModelVersion()

What it means

DefaultModelXmlFactory.read enforces that models with modelVersion greater than 4.0.0 must carry an XML namespace starting with http://maven.apache.org/POM/. This guards the Maven 4 consumed POM format: a 4.1+ model without the official namespace (wrong URI, or namespace-less XML) is rejected with XmlReaderException before the model is returned.

Source

Thrown at impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultModelXmlFactory.java:68

import org.apache.maven.api.xml.XmlService;
import org.apache.maven.model.v4.MavenStaxReader;
import org.apache.maven.model.v4.MavenStaxWriter;

import static java.util.Objects.requireNonNull;
import static org.apache.maven.impl.StaxLocation.getLocation;
import static org.apache.maven.impl.StaxLocation.getMessage;

@Named
@Singleton
public class DefaultModelXmlFactory implements ModelXmlFactory {
    @Override
    @Nonnull
    public Model read(@Nonnull XmlReaderRequest request) throws XmlReaderException {
        requireNonNull(request, "request");
        Model model = doRead(request);
        if (isModelVersionGreaterThan400(model)
                && !model.getNamespaceUri().startsWith("http://maven.apache.org/POM/")) {
            throw new XmlReaderException(
                    "Invalid namespace '" + model.getNamespaceUri() + "' for model version " + model.getModelVersion(),
                    null,
                    null);
        }
        return model;
    }

    private boolean isModelVersionGreaterThan400(Model model) {
        String version = model.getModelVersion();
        if (version == null) {
            return false;
        }
        try {
            String[] parts = version.split("\\.");
            int major = Integer.parseInt(parts[0]);
            int minor = parts.length > 1 ? Integer.parseInt(parts[1]) : 0;
            return major > 4 || (major == 4 && minor > 0);
        } catch (NumberFormatException | IndexOutOfBoundsException e) {

View on GitHub (pinned to e4093d4e12)

Solutions

1. Declare the official namespace on the root element: <project xmlns="http://maven.apache.org/POM/4.1.0" ...> with matching xsi:schemaLocation
2. Keep modelVersion at 4.0.0 if you cannot add the namespace (the check only applies above 4.0.0)
3. When writing models programmatically, use ModelXmlFactory.write so the correct namespace is emitted

Example fix

<!-- before -->
<project>
  <modelVersion>4.1.0</modelVersion>
  ...

<!-- after -->
<project xmlns="http://maven.apache.org/POM/4.1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
  <modelVersion>4.1.0</modelVersion>
  ...

// before reading a 4.1+ POM, verify the root namespace
var factory = javax.xml.XMLInputFactory.newInstance();
try (var r = factory.createXMLStreamReader(Files.newInputStream(pom))) {
    r.nextTag();
    if (!'http://maven.apache.org/POM/'.regionMatches(
            true, 0, r.getNamespaceURI() == null ? '' : r.getNamespaceURI(), 0, Math.min(27, r.getNamespaceURI() == null ? 0 : r.getNamespaceURI().length()))) {
        throw new IllegalArgumentException('POM must use the http://maven.apache.org/POM/ namespace');
    }
}

When it happens

Trigger: Reading a pom.xml whose <project> root declares modelVersion 4.1.0 (or higher) but omits xmlns or uses a different namespace (e.g. a custom schema or the 4.0.0 namespace with a 4.1.0 modelVersion); hand-generated POMs written by tools that drop the xmlns attribute.

Common situations: Programmatically generated POMs missing the xmlns attribute; upgrading modelVersion to 4.1.0 while keeping an old/no namespace; transforming POMs with XML tooling that strips namespaces; copy-pasting a 4.1 skeleton from a blog that omitted xmlns.

Related errors

• path, url, reader or inputStream must be non null
• Unable to read model:
• Repository list contains duplicate entries. Each repository
• Repository list contains null entries. All repository entrie
• Cannot read metadata from '{}': {}

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/f924b4a65d606683. Report an issue: GitHub.