如何更新在Java中使用MAP的XML文件

我有一个XML文件（xyz.xml），示例数据如下所示：

我想从文件（xyz.xml）中读取并更新同一xml文件中的值。

注意（我有一些变量，这些变量将包含用于更新xml文件的数据）

我的场景的简要说明[我将首先从另一个XML文件中读取值，并将它们存储在变量中。然后，我将使用变量来更新第二个xml文件（xyz.zml）

即使使用其他方法，如何在Java中完成此操作（写入XML文件（xyz.xml））？

<?xml version="1.0" encoding="UTF-8"?>
<map xmlns="http://www.w3.org/2005/xpath-functions">
   <string key="ankomstDato">2019-06-03T09:24:40.486</string>
   <boolean key="samletUsrHoey">true</boolean>
   <array key="driftsform">
      <string>string_value</string>
   </array>
   <number key="versjon">0</number>
</map>

我的示例Java代码，但我得到了

线程“主”中的异常java.lang.NullPointerException，位于no.difi.oauth2.utils.SolutionXML2XmlFormat.Write2XMLfile（SolutionXML2XmlFormat.java:68）

import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
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.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
//** */

public class SolutionXML2XmlFormat {
    //Create Public Variables to store data
    //**
    public static String ankomstDato_value;
    public static String art_value;
        
    //+++

    public void Xml2JavaObject(String TheXMLPath){
        //read the xml(TheXMLPath) and store values in variables

        //This is just an example
        ankomstDato_value = "2022-08-03T09:24:40.486";
                   
        //Call method to write values
        Write2XMLfile();
    }
    
    //Modify the existing values in Api_XML_Format.xml
    //*
    public void Write2XMLfile(){
        try {
            String filepath = "src/main/java/no/difi/oauth2/utils/Api_XML_Format.xml";
            DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
            Document doc = docBuilder.parse(filepath);
    
            // Get the root element , this case its "map"
            Node map = doc.getFirstChild();

            //1. ankomstDato
            Node ankomstDato = doc.getElementsByTagName("ankomstDato").item(0);
            ankomstDato.setTextContent(ankomstDato_value);
            //End ankomstDato
            
            //2. art
            //Node art = doc.getElementsByTagName("art").item(0);
            //art.setTextContent(art_value);
            //End art

            // write the content into xml file
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(new File(filepath));
            transformer.transform(source, result);
    
            System.out.println("Done Update The Api_XML_Format.xml");
    
           } catch (ParserConfigurationException pce) {
            pce.printStackTrace();
           } catch (TransformerException tfe) {
            tfe.printStackTrace();
           } catch (IOException ioe) {
            ioe.printStackTrace();
           } catch (SAXException sae) {
            sae.printStackTrace();
        }
    }


    
}