Query XML with Namespaces in Java Using XPath

When working with XML documents containing elements bound to namespaces, querying with XPath can become challenging. Consider the following example:

Using a default "no namespace" XPath expression like "/workbook/sheets/sheet[1]" will fail. This is because the elements in the XML document are bound to a namespace, which is not considered in the XPath expression.

Solution 1: Register Namespace and Use Namespace Prefix

The recommended approach is to register the namespace with a namespace prefix, making XPath easier to read and maintain:

NamespaceContext namespaceContext = new NamespaceContext() {
    @Override
    public String getNamespaceURI(String prefix) {
        if (prefix.equals("main")) {
            return "http://schemas.openxmlformats.org/spreadsheetml/2006/main";
        } else if (prefix.equals("r")) {
            return "http://schemas.openxmlformats.org/officeDocument/2006/relationships";
        }
        return null;
    }
};
XPathFactory xPathFactory = XPathFactory.newInstance();
XPath xPath = xPathFactory.newXPath();
xPath.setNamespaceContext(namespaceContext);

NodeList nodes = (NodeList) xPath.evaluate("/main:workbook/main:sheets/main:sheet[1]", document, XPathConstants.NODESET);

Using the namespace prefix, the XPath expression becomes "/main:workbook/main:sheets/main:sheet[1]", which correctly addresses elements bound to the specified namespace.

Solution 2: Generic Match and Predicate Filter

Alternatively, an XPath expression without a namespace prefix can be constructed by using a generic match for the element and a predicate filter that specifies the desired local-name() and namespace-uri():

XPathFactory xPathFactory = XPathFactory.newInstance();
XPath xPath = xPathFactory.newXPath();

NodeList nodes = (NodeList) xPath.evaluate("/*[local-name()='workbook' and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main']"  
        "/*[local-name()='sheets' and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main']"  
        "/*[local-name()='sheet' and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main'][1]",
        document, XPathConstants.NODESET);

This method is verbose and can present risks if mixed vocabularies are present in the XML document.

Conclusion

When dealing with XML documents with namespaces, it is essential to consider namespace bindings. By registering the namespace with a prefix or carefully crafting generic XPath expressions, accurate and reliable queries can be performed.