Pulling value from an xml file using DocumentBuilder

I'm accessing ALM via their REST APIs. I confess I'm not the strongest with xml yet but this is my attempt. The response returned to me looks like:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Entities TotalResults="1">
    <Entity Type="test-instance">
        <ChildrenCount>
            <Value>0</Value>
        </ChildrenCount>
        <Fields>
            <Field Name="test-id">
                <Value>13392</Value>
            </Field>
            <Field Name="os-config">
                <Value/>
            </Field>
            <Field Name="data-obj">
                <Value/>
            </Field>
            <Field Name="is-dynamic">
                <Value>N</Value>
            </Field>
            <Field Name="exec-time">
                <Value>09:41:40</Value>
            </Field>
            <Field Name="cycle">
                <Value/>
            </Field>
            <Field Name="has-linkage">
                <Value>N</Value>
            </Field>
            <Field Name="exec-event-handle">
                <Value/>
            </Field>
            <Field Name="exec-date">
                <Value>2019-06-12</Value>
            </Field>
            <Field Name="last-modified">
                <Value>2019-06-12 06:42:47</Value>
            </Field>
            <Field Name="subtype-id">
                <Value>hp.qc.test-instance.VAPI-XP-TEST</Value>
            </Field>
            <Field Name="cycle-id">
                <Value>5421</Value>
            </Field>
            <Field Name="attachment">
                <Value/>
            </Field>
            <Field Name="id">
                <Value>13404</Value>
            </Field>
            <Field Name="plan-scheduling-date"/>
            <Field Name="assign-rcyc">
                <Value/>
            </Field>
            <Field Name="test-config-id">
                <Value>14751</Value>
            </Field>
            <Field Name="owner">
                <Value>johnsmith</Value>
            </Field>
            <Field Name="pinned-baseline">
                <Value/>
            </Field>
            <Field Name="ver-stamp">
                <Value>4</Value>
            </Field>
            <Field Name="test-instance">
                <Value>1</Value>
            </Field>
            <Field Name="host-name">
                <Value/>
            </Field>
            <Field Name="order-id">
                <Value>1</Value>
            </Field>
            <Field Name="eparams">
                <Value/>
            </Field>
            <Field Name="task-status">
                <Value/>
            </Field>
            <Field Name="iterations">
                <Value/>
            </Field>
            <Field Name="environment">
                <Value/>
            </Field>
            <Field Name="actual-tester">
                <Value>johnsmith</Value>
            </Field>
            <Field Name="name">
                <Value>My Test Case</Value>
            </Field>
            <Field Name="bpta-change-awareness">
                <Value/>
            </Field>
            <Field Name="user-template-02"/>
            <Field Name="plan-scheduling-time">
                <Value/>
            </Field>
            <Field Name="user-02">
                <Value/>
            </Field>
            <Field Name="status">
                <Value>Passed</Value>
            </Field>
        </Fields>
        <RelatedEntities/>
    </Entity>
    <singleElementCollection>false</singleElementCollection>
</Entities>

I'm trying to get the value from first field, "test-id" near the top of the file.

I've tried to pull the value using DocumentBuilder:

DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
InputSource src = new InputSource();
src.setCharacterStream(new StringReader(response.toString()));  <--response.toString() is the xml data you see above.

Document doc = builder.parse(src);
test_id = doc.getElementsByTagName("test-id").item(0).getTextContent();

Unfortunately that last line equates to nothing. Can someone give me a little push here? I'm not sure what else to try.

Solution

This is how it would look using XPath:

InputSource src = new InputSource();
src.setCharacterStream(new StringReader(response.toString()));

DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document doc = builder.parse(src);

XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile("//Field[@Name='test-id']/Value");

System.out.println(expr.evaluate(doc, XPathConstants.STRING));

A full explanation of XPath expression syntax is beyond the scope of this answer, but:

//Field - Find all Field elements no matter where they are in the document...
[@Name='test-id'] ... that have a Name attribute with the value test-id...
/Value ... and of those, give me the Value element(s) that are child nodes of those matching Fields

Alternatively you can also be very explicit about the path to the node you are looking for (instead of using //):

XPathExpression expr = xpath.compile("/Entities/Entity/Fields/Field[@Name='test-id']/Value");