How to compare 2 XML DOM Element / Documents

xml-dom-comparation.md

How to compare 2 XML DOM Elements / Documents

As using elements directly to compare will cause issues in case you have prefixes and don't wish to import the whole xml, you can compare sections of xml (Element) this way.

Dependencies

• W3C DOM (Included in Java 16) For testing
• XMLUnit Core
• XMLUnit Matchers
• Hamcrest
• JUnit

File build.gradle

[...]
dependencies {
    implementation 'org.glassfish.jaxb:jaxb-runtime:3.0.2'

    testImplementation 'org.xmlunit:xmlunit-core:2.9.0'
    testImplementation 'org.xmlunit:xmlunit-matchers:2.9.0'
    testImplementation 'org.hamcrest:hamcrest:2.2'

    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.1'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.1'
}
[...]

Setup

Create a @beforeAll which is going to create the document builder in a test class.

class DOMTest {
  private static DocumentBuilder documentBuilder;

    @BeforeAll
    static void setup() throws ParserConfigurationException {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        documentBuilder = documentBuilderFactory.newDocumentBuilder();
    }
 
 [...]
 
}

Tests

Comparing 2 external files as Document

@Test
void compare2externalFiles() throws IOException, SAXException {
Document fileA = documentBuilder.parse(
            getClass().getClassLoader().getResourceAsStream("fileA.xml"));
Document fileB = documentBuilder.parse(
            getClass().getClassLoader().getResourceAsStream("fileB.xml"));

assertThat(
            expected, CompareMatcher.isIdenticalTo(doc2).ignoreWhitespace()
        );
}

Comparing an external file with an internal Element

WARNING: The document must be the same used to create your element.

@Test
    void compareExternalWithInternal() throws IOException, SAXException {
        Document fileA = documentBuilder.parse(
                getClass().getClassLoader().getResourceAsStream("fileA.xml"));
        Document document = documentBuilder.newDocument(); // must be the same document used to create the element.
        document.appendChild(null); //replace null with the XML element you want there

        assertThat(
                fileA, CompareMatcher.isIdenticalTo(document).ignoreWhitespace()
        );
    }

Comparing 2 internal Elements

WARNING: The document must be the same used to create your element.

    @Test
    void compare2Internals() {
        Document documentA = documentBuilder.newDocument(); // must be the same document used to create the element.
        documentA.appendChild(elementA); //replace with the XML element you want there

        Document documentB = documentBuilder.newDocument();
        documentB.appendChild(elementB);

        assertThat(
                documentA, CompareMatcher.isIdenticalTo(documentB).ignoreWhitespace()
        );
    }