如何在java中将孩子附加到xml后保存它？

import org.w3c.dom.*;
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.*;

public class XMLWriter {
    public static void main(String[] args) {
        try {
            // 创建一个空的Document对象
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document doc = builder.newDocument();

            // 创建一个根元素节点
            Element rootElement = doc.createElement("root");
            doc.appendChild(rootElement);

            // 创建一个孩子节点
            Element childElement = doc.createElement("child");
            childElement.setAttribute("name", "Alice");
            rootElement.appendChild(childElement);

            // 将XML文档保存到文件
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(new File("output.xml"));
            transformer.transform(source, result);

            System.out.println("XML文件保存成功！");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}