Java uses the DOM to create XML and append content to the original XML.

Create new xml file

step:

1. Get the factory instance DocumentBuilderFactory of the DOM parser

2. Get the DOM parser from the DOM factory

3 Create a DOM tree

4 Create a node, add a node

5 Add the node you just created to another node

6 Add the node to the document

7 Save the xml file

Code:

// 1. Get the factory instance of the DOM parser  
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
        // 2. Get the DOM parser from the DOM factory  
        DocumentBuilder db;
		try {
	        db = dbf.newDocumentBuilder();
	        Document docs = db.newDocument();
	        //create node  
	        Element noteElement = docs.createElement("note");  
	        Element toElement =  docs.createElement("to");  
	        Text l = docs.createTextNode("333");  
	        toElement.appendChild(l);//lableElement.setNodeValue(lable);  
	        Element fromElement =  docs.createElement("from");  
	        Text t = docs.createTextNode("321");  
	        fromElement.appendChild(t);//titleElement.setNodeValue(title);  
	        Element headingElement =  docs.createElement("heading");  
	        Text x = docs.createTextNode("sadda");  
	        headingElement.appendChild(x);//textElement.setNodeValue(text);
	        
	        String time=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss").format(new Date());
	        Element bodyElement =  docs.createElement("body");  
	        Text m = docs.createTextNode(time);  
	        bodyElement.appendChild(m);  
	          
	        //Add parent-child relationship  
	        noteElement.appendChild(toElement);  
	        noteElement.appendChild(fromElement);  
	        noteElement.appendChild(headingElement);  
	        noteElement.appendChild(bodyElement);  
	        //Element docsElement=(Element)docs.getElementsByTagName("docs").item(0);  
	        //docsElement.appendChild(docElement);  
	        //Add the node to the document
	        docs.getDocumentElement().appendChild(noteElement);  
	          
	        //save the xml file  
	        TransformerFactory transformerFactory=TransformerFactory.newInstance();  
	        Transformer transformer=transformerFactory.newTransformer();  
	        DOMSource domSource=new DOMSource(docs);  
	          
	        //set encoding type  
	        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");  
	        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
	        File f=new File("e:\\Test.xml");
	        StreamResult result=new StreamResult(new FileOutputStream(f));  
	          
	        //Convert DOM tree to xml file  
	        transformer.transform(domSource, result);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace ();
		}  
       
	}

Additional content:

package com.test;

import java.io.File;
import java.io.FileOutputStream;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
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.Text;

public class TestXml {
	public static void main(String[] args) {
		
         // 1. Get the factory instance of the DOM parser  
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
        // 2. Get the DOM parser from the DOM factory  
        DocumentBuilder db;
	try {
		db = dbf.newDocumentBuilder();
		// 3. Parse the XML document to get the DOM tree  
	        File f=new File("e:\\Test.xml");
	        Document docs = db.parse(f);  
	        
	        //create node  
	        Element noteElement = docs.createElement("note");  
	        Element toElement =  docs.createElement("to");  
	        Text l = docs.createTextNode("333");  
	        toElement.appendChild(l);//lableElement.setNodeValue(lable);  
	        Element fromElement =  docs.createElement("from");  
	        Text t = docs.createTextNode("321");  
	        fromElement.appendChild(t);//titleElement.setNodeValue(title);  
	        Element headingElement =  docs.createElement("heading");  
	        Text x = docs.createTextNode("sadda");  
	        headingElement.appendChild(x);//textElement.setNodeValue(text);
	        
	        String time=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss").format(new Date());
	        Element bodyElement =  docs.createElement("body");  
	        Text m = docs.createTextNode(time);  
	        bodyElement.appendChild(m);  
	          
	        //Add parent-child relationship  
	        noteElement.appendChild(toElement);  
	        noteElement.appendChild(fromElement);  
	        noteElement.appendChild(headingElement);  
	        noteElement.appendChild(bodyElement);  
	        
	        docs.getDocumentElement().appendChild(noteElement);  
	          
	        //save the xml file  
	        TransformerFactory transformerFactory=TransformerFactory.newInstance();  
	        Transformer transformer=transformerFactory.newTransformer();  
	        DOMSource domSource=new DOMSource(docs);  
	          
	        //set encoding type  
	        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");  
	        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
	        StreamResult result=new StreamResult(new FileOutputStream(f));  
	          
	        //Convert DOM tree to xml file  
	        transformer.transform(domSource, result);
	} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace ();
		}  
       
	}
}