怎么向已有xml文件添加数据

import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import org.jdom.Attribute;import org.jdom.Comment;import org.jdom.Document;import org.jdom.Element;import org.jdom.output.Format;import org.jdom.output.XMLOutputter;public class JDomOutput{    public static void main(String[] args) throws IOException    {        //创建文档        Document document = new Document();        //创建根元素        Element people = new Element("people");        //把根元素加入到document中        document.addContent(people);                 //创建注释        Comment rootComment = new Comment("将数据从程序输出到XML中！");        people.addContent(rootComment);                //创建父元素        Element person1 = new Element("person");        //把元素加入到根元素中        people.addContent(person1);        //设置person1元素属性        person1.setAttribute("id", "001");                Attribute person1_gender = new Attribute("gender", "male");        person1.setAttribute(person1_gender);                Element person1_name = new Element("name");        person1_name.setText("刘德华");        person1.addContent(person1_name);                Element person1_address = new Element("address");        person1_address.setText("香港");        person1.addContent(person1_address);                        Element person2 = new Element("person");        people.addContent(person2);                person2.setAttribute("id", "002").setAttribute("gender","male");//添加属性，可以一次添加多个属性                Element person2_name = new Element("name");        person2_name.setText("林志颖");        person2.addContent(person2_name);                Element person2_address = new Element("address");        person2_address.setText("台湾");        person2.addContent(person2_address);                        //设置xml输出格式        Format format = Format.getPrettyFormat();        format.setEncoding("utf-8");//设置编码        format.setIndent("    ");//设置缩进                        //得到xml输出流        XMLOutputter out = new XMLOutputter(format);        //把数据输出到xml中        out.output(document, new FileOutputStream("jdom.xml"));//或者FileWriter            }}