如何将替换的更改追加到XML节点？

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XMLUpdater {
    public static void main(String[] args) {
        try {
            // 加载XML文件
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document document = builder.parse("input.xml");

            // 定位目标节点
            NodeList nodeList = document.getElementsByTagName("book");
            for (int i = 0; i < nodeList.getLength(); i++) {
                Element book = (Element) nodeList.item(i);

                // 替换节点内容
                Element title = (Element) book.getElementsByTagName("title").item(0);
                title.setTextContent("New Title");

                // 追加更改
                Element author = document.createElement("author");
                author.setTextContent("John Doe");
                book.appendChild(author);
            }

            // 保存修改后的XML文件
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(document);
            StreamResult result = new StreamResult("output.xml");
            transformer.transform(source, result);

            System.out.println("XML更新成功！");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}