Getting child node while parcing xml in java

i am parsing xml file with DOM. Each book can have multiple authors. i can't get access to author tags, what am i doing wrong? how to get child nodes correctly?

This is my java code:

public class DOMBooksReader {

    private Book book;
    private Author author;
    private ArrayList<Book> books = new ArrayList<Book>();
    SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy", Locale.ENGLISH);

    public static void main(String[] args) throws ParseException {

        DOMBooksReader domBooksReader = new DOMBooksReader();
        domBooksReader.parseXml(new File("src\\books.xml"));

    }

    public void parseXml(File file) throws ParseException {

        Document doc = null;
        try {
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            doc = documentBuilder.parse(file);
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        assert doc != null;
        NodeList bookNodes = doc.getElementsByTagName("book");

        for (int i = 0; i < bookNodes.getLength(); i++) {
            book = new Book();
            books.add(book);


            }

            if (bookElement.getNodeName().equals("authors")) {
                NodeList authorNodes = bookElement.getChildNodes();
                for (int j = 0; j < authorNodes.getLength(); j++) {
                    author = new Author();
                    book.getAuthors().add(author);

                }
            }


        }
    }

Here is XML:

<?xml version="1.0" encoding="UTF-8"?>
<books>
    <book>
        <name>Capacity Planning for Web Performance: Metrics, Models, and Methods</name>
        <authors>
            <author>
                <firstName>Daniel</firstName>
                <lastName>Menasce</lastName>
                <middleInitial>A</middleInitial>
            </author>
            <author>
                <firstName>Virgilo</firstName>
                <lastName>Almeida</lastName>
                <middleInitial>F</middleInitial>
            </author>
        </authors>
...