How to access to value read XML using XPath in Java

Question

I want to read XML data using XPath in Java.

I have the next XML file named MyXML.xml:

<?xml version="1.0" encoding="iso-8859-1" ?>
<REPOSITORY xmlns:LIBRARY="http://www.openarchives.org/LIBRARY/2.0/"
            xmlns:xsi="http://www.w3.prg/2001/XMLSchema-instance"
            xsi:schemaLocation="http://www.openarchives.org/LIBRARY/2.0/ http://www.openarchives.org/LIBRARY/2.0/LIBRARY-PHM.xsd">
    <repository>Test</repository>
    <records>
        <record>
            <ejemplar>
                <library_book:book
                        xmlns:library_book="http://www.w3c.es/LIBRARY/book/"
                        xmlns:book="http://www.w3c.es/LIBRARY/book/"
                        xmlns:bookAssets="http://www.w3c.es/LIBRARY/book/"
                        xmlns:bookAsset="http://www.w3c.es/LIBRARY/book/"
                        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                        xsi:schemaLocation="http://www.w3c.es/LIBRARY/book/ http://www.w3c.es/LIBRARY/replacement/book.xsd">
                    <book:bookAssets count="1">
                        <book:bookAsset nasset="1">
                            <book:bookAsset.id>value1</book:bookAsset.id>
                            <book:bookAsset.event>
                                <book:bookAsset.event.id>value2</book:bookAsset.event.id>
                            </book:bookAsset.event>
                        </book:bookAsset>
                    </book:bookAssets>
                </library_book:book>
            </ejemplar>
        </record>
    </records>
</REPOSITORY>

I want access to value1 and value2 values. For this, I try this:

// Standard of reading a XML file
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder;
Document doc = null;
XPathExpression expr = null;
builder = factory.newDocumentBuilder();
doc = builder.parse("MyXML.xml");

// Create a XPathFactory
XPathFactory xFactory = XPathFactory.newInstance();

// Create a XPath object
XPath xpath = xFactory.newXPath();

expr = xpath.compile("//REPOSITORY/records/record/ejemplar/library_book:book//book:bookAsset.event.id/text()");

Object result = expr.evaluate(doc, XPathConstants.STRING);

System.out.println("RESULT=" + (String)result);

But I don't get any results. Only prints RESULT=.

¿How to access to value1 and value2 values?. ¿What is the XPath filter to apply?.

Thanks in advanced.

I'm using JDK6.

Answer 1

One approach is to implement a name space context like:

public static class UniversalNamespaceResolver implements NamespaceContext {
    private Document sourceDocument;


    public UniversalNamespaceResolver(Document document) {
        sourceDocument = document;
    }


    public String getNamespaceURI(String prefix) {
        if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) {
            return sourceDocument.lookupNamespaceURI(null);
        } else {
            return sourceDocument.lookupNamespaceURI(prefix);
        }
    }


    public String getPrefix(String namespaceURI) {
        return sourceDocument.lookupPrefix(namespaceURI);
    }

    public Iterator getPrefixes(String namespaceURI) {
        return null;
    }

}

And then use it like

        xpath.setNamespaceContext(new UniversalNamespaceResolver(doc));

You also need to move up all the namespace declarations to the root node (REPOSITORY). Otherwise it might be a problem if you have namespace declarations on two different levels.

Answer 2

You are having problems with namespaces, what you can do is

1. take them into account
2. ignore them using the XPath local-name() function

Solution 1 implies implementing a NamespaceContext that maps namespaces names and URIs and set it on the XPath object before querying.

Solution 2 is easy, you just need to change your XPath (but depending on your XML you may fine-tune your XPath to be sure to select the correct element):

XPath xpath = xFactory.newXPath();
expr = xpath.compile("//*[local-name()='bookAsset.event.id']/text()");
Object result = expr.evaluate(doc, XPathConstants.STRING);
System.out.println("RESULT=" + result);

Runnable example on ideone.

You can take a look at the following blog article to better understand the uses of namespaces and XPath in Java (even if old)

Answer 3

Try

Object result = expr.evaluate(doc, XPathConstants.NODESET);

    // Cast the result to a DOM NodeList
    NodeList nodes = (NodeList) result;
    for (int i=0; i<nodes.getLength();i++){
      System.out.println(nodes.item(i).getNodeValue());
    }