如何在java中修改xml文档并将其作为字符串返回？

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

public class XMLUtils {
    public static String modifyXML(String xmlString, String elementName, String newValue) {
        try {
            // 创建解析器工厂和解析器
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();

            // 解析XML字符串
            Document doc = builder.parse(new InputSource(new StringReader(xmlString)));

            // 获取需要修改的节点列表
            NodeList nodes = doc.getElementsByTagName(elementName);

            // 遍历节点并修改值
            for (int i = 0; i < nodes.getLength(); i++) {
                Node node = nodes.item(i);
                node.setTextContent(newValue);
            }

            // 将修改后的XML转换为字符串
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StringWriter writer = new StringWriter();
            StreamResult result = new StreamResult(writer);
            transformer.transform(source, result);
            String modifiedXML = writer.toString();

            return modifiedXML;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}