Various XML utilities, such as unmarshal and consume XML input stream by target element name (and -optional- target element depth).

XmlUtils.java

import lombok.AccessLevel;
import lombok.NoArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.util.StreamReaderDelegate;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import java.io.InputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.function.Consumer;

@Slf4j
@NoArgsConstructor(access = AccessLevel.PRIVATE)
public final class XmlUtils {

    public static <T> void unMarshalAndConsume(InputStream inputStream, Class<T> targetClass, String targetElementName, Consumer<T> consumer) throws Exception {
        unMarshalAndConsume(inputStream, targetClass, targetElementName, null, consumer);
    }

    public static <T> void unMarshalAndConsume(InputStream inputStream, Class<T> targetClass, String targetElementName, Integer targetElementDepth, Consumer<T> consumer) throws Exception {
        XMLStreamReader xmlStreamReader = null;
        try {
            final XMLInputFactory xmlInputFactory = XMLInputFactory.newFactory();
            xmlStreamReader = xmlInputFactory.createXMLStreamReader(inputStream);

            final Unmarshaller unmarshaller = JAXBContext.newInstance(targetClass).createUnmarshaller();

            int currentDepth = 0;
            while (xmlStreamReader.hasNext()) {
                xmlStreamReader.next();

                if (xmlStreamReader.isStartElement()) {
                    currentDepth++;

                    if (xmlStreamReader.getLocalName().equals(targetElementName) && (Objects.isNull(targetElementDepth) || targetElementDepth == currentDepth)) {
                        T value = unmarshaller.unmarshal(xmlStreamReader, targetClass).getValue();
                        consumer.accept(value);
                    }
                } else if (xmlStreamReader.isEndElement()) {
                    currentDepth--;
                }
            }
        } finally {
            if (xmlStreamReader != null) {
                xmlStreamReader.close();
            }
        }
    }

    public static <T> List<T> unMarshalAndList(InputStream inputStream, Class<T> targetClass, String targetElementName) throws Exception {
        return unMarshalAndList(inputStream, targetClass, targetElementName, null);
    }

    public static <T> List<T> unMarshalAndList(InputStream inputStream, Class<T> targetClass, String targetElementName, Integer targetElementDepth) throws Exception {
        final List<T> results = new ArrayList<>();
        unMarshalAndConsume(inputStream, targetClass, targetElementName, targetElementDepth, results::add);
        return results;
    }

    public static String toString(Source xmlSource) {
        try {
            final StringWriter writer = new StringWriter();
            final StreamResult result = new StreamResult(writer);
            final Transformer transformer = TransformerFactory.newInstance().newTransformer();
            transformer.transform(xmlSource, result);
            return writer.toString();
        } catch (TransformerException e) {
            throw new RuntimeException("XML source couldn't be transformed to String", e);
        }
    }

    public static <T> T unMarshalToTypeByIgnoringNameSpace(Source xmlSource, Class<T> targetClass) throws Exception {
        final NameSpaceIgnoringXMLStreamReader streamReader = new NameSpaceIgnoringXMLStreamReader(XMLInputFactory.newFactory().createXMLStreamReader(xmlSource));
        final Unmarshaller unmarshaller = JAXBContext.newInstance(targetClass).createUnmarshaller();
        return unmarshaller.unmarshal(streamReader, targetClass).getValue();
    }

    static class NameSpaceIgnoringXMLStreamReader extends StreamReaderDelegate {

        public NameSpaceIgnoringXMLStreamReader(XMLStreamReader reader) {
            super(reader);
        }

        @Override
        public String getAttributeNamespace(int arg0) {
            return StringUtils.EMPTY;
        }

        @Override
        public String getNamespaceURI() {
            return StringUtils.EMPTY;
        }

    }

}