Xpath Java get element by testing value

Question

I'm trying to use Xpath to parse an xml string, but i don't know how use the expression to retrieve what i want.

I have the following xml content :

<root1>
    <root2>
        <A>something</A>
        <B>something</B>
        <C>
            <D>
                <E>DataE</E>
                <F>DataF</F>
                <G>something</G>
                <H>something</H>
                <I>
                    <J>
                      <K>DataK</K>
                      <L>DataL</L>
                    </J>
                </I>
            </D>
            <D>
                <E>DataE_ERROR</E>
                <F>DataF</F>
                <G>something</G>
                <H>something</H>
                <I>
                    <J>
                      <K>DataK</K>
                      <L>DataL</L>
                    </J>
                </I>
            </D>
        </C>
     </root2>
</root1>

I would like to get the value of F,K,L when the value of E is DataE for example.

I'm using for this Xpath but i can't find the good expression !

here is my java code :

public void getit()
{
    String xml = "The xml above";

    DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
    DocumentBuilder b = f.newDocumentBuilder();
    Document d = b.parse(new InputSource(new StringReader(xml)));
    d.getDocumentElement().normalize();

    // No idea ! how can i make it work by testing the value of E
    String expression = "//E/text()|//F/text()|//K/text()|//L/text()";

    XPath xPath = XPathFactory.newInstance().newXPath();
    Object result = xPath.compile(expression).evaluate(d, XPathConstants.NODESET);

    NodeList nodes = (NodeList) result;
    for (int i = 0; i < nodes.getLength(); i++) {
        System.out.println(nodes.item(i).getNodeValue()); 
    }

}

Answer 1

Just so I could ensure the query was working, I modified the example XML as follows...

<root1>
    <root2>
        <A>something</A>
        <B>something</B>
        <C>
            <D>
                <E>DataE</E>
                <F>DataF 1</F>
                <G>something</G>
                <H>something</H>
                <I>
                    <J>
                        <K>DataK 1</K>
                        <L>DataL 1</L>
                    </J>
                </I>
            </D>
            <D>
                <E>DataE_ERROR</E>
                <F>DataF 2</F>
                <G>something</G>
                <H>something</H>
                <I>
                    <J>
                        <K>DataK 2</K>
                        <L>DataL 2</L>
                    </J>
                </I>
            </D>
        </C>
    </root2>
</root1>

The magic is here...

String expression = "//F[ancestor::D/E[text()='DataE']]|//K[ancestor::D/E[text()='DataE']]|//L[ancestor::D/E[tex

Basically, this reads...

Find any F node, who has an ancestor that contains D with a child of E whose text is equal to DataE or ...

Now, this is important, you could use ../ to find the parent node, but K and L are buried in sub nodes and I'm not sure if they might be deeper or shallow, so I went for this method.

You might need to refine it a bit, but I took the relationship of D/E as been important.

With this (and the example below), I was able to generate the following output...

Found DataF 1
Found DataK 1
Found DataL 1

Runnable example:

public class TestXPath {

    public static void main(String[] args) {
        String xml = "The xml above";

        try {
            DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
            DocumentBuilder b = f.newDocumentBuilder();
            Document d = b.parse(new File("Values.xml"));
            d.getDocumentElement().normalize();

            String expression = "//F[ancestor::D/E[text()='DataE']]|//K[ancestor::D/E[text()='DataE']]|//L[ancestor::D/E[text()='DataE']]";
            XPath xPath = XPathFactory.newInstance().newXPath();
            Object result = xPath.compile(expression).evaluate(d, XPathConstants.NODESET);

            NodeList nodes = (NodeList) result;
            for (int i = 0; i < nodes.getLength(); i++) {

                Node node = nodes.item(i);
                System.out.println("Found " + node.getTextContent());
            }
        } catch (ParserConfigurationException | SAXException | IOException | XPathExpressionException | DOMException exp) {
            exp.printStackTrace();
        }
    }

}