Java HTML/XML - 如何使用DOM创建XML中的新元素

import java.io.File;
import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

public class Main {
  public static void sendXml(String result, int operationN) throws Exception{
    String filepath = "file.xml";
    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
    Document doc = docBuilder.parse(filepath);

    Node tonode = doc.getElementsByTagName("command").item(0);
    Element res = doc.createElement("result");
    res.setTextContent(result);
    tonode.appendChild(res);
    TransformerFactory transformerFactory = TransformerFactory.newInstance();
    Transformer transformer = transformerFactory.newTransformer();
    DOMSource source = new DOMSource(doc);
    StreamResult result1 = new StreamResult(new File("file2.xml"));

    StreamResult result3 = new StreamResult(System.out);
    transformer.transform(source, result1);
  }
  public static void main(String argv[]) throws Exception {
    sendXml("hitest", 1);
  }
}