下面的代码插入方法出错了   不知道是什么问题

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import org.jdom.Document;
import org.jdom.Element;
import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;
import org.jdom.output.Format;
import org.jdom.output.XMLOutputter;

// 写入xml文件
public class WriteXML {
    static int i=0;
    Element people0;
    Element root, name, nickname, pass,love,city,six,jieshao;
    public  void wirteXml(){
    
        root = new Element("people-info"); //生成根元素：people-info 
        i++;
        people0 = new Element("people"+i); 
        name = new Element("name");
        nickname = new Element("nickname");
        pass = new Element("pass");
        love=new Element("love");
        city=new Element("city");
        six=new Element("six");
        jieshao=new Element("jieshao");
        Document doc = new Document(root); //将根元素植
        name.setText("11111111");
//        name.setText(people.name);
//        nickname.setText(people.nickname);
//        pass.setText(people.pass);
//        love.setText(people.love);
//        city.setText(people.city);
//        six.setText(people.six);
//        jieshao.setText(people.jieshao);
        
        people0.addContent(name);
        people0.addContent(nickname);
        people0.addContent(pass);
        people0.addContent(love);
        people0.addContent(city);
        people0.addContent(six);
        people0.addContent(jieshao);
        
        root.addContent(people0);
         
        Format format = Format.getCompactFormat();
        format.setEncoding("gb2312"); //设置xml文件的字符为gb2312
        format.setIndent("    "); //设置xml文件的缩进为4个空格
        XMLOutputter XMLOut = new XMLOutputter(format);//在元素后换行，每一层元素缩排四格     
        try {
            XMLOut.output(doc, new FileOutputStream("E:\\book\\zhuce\\people-info.xml"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    
        }
public  void insert(){
    i++;
     SAXBuilder builder = new SAXBuilder();

     Document read_doc=null;
        try {
            read_doc = builder.build("E:\\book\\zhuce\\people-info.xml");
        } catch (JDOMException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    Element stu = read_doc.getRootElement();
    people0 = new Element("people"+i); 
    name = new Element("name");
    nickname = new Element("nickname");
    pass = new Element("pass");
    love=new Element("love");
    city=new Element("city");
    six=new Element("six");
    jieshao=new Element("jieshao");
    //Document doc = new Document(root); //将根元素植
    name.setText("22222222222");
//    name.setText(people.name);
//    nickname.setText(people.nickname);
//    pass.setText(people.pass);
//    love.setText(people.love);
//    city.setText(people.city);
//    six.setText(people.six);
//    jieshao.setText(people.jieshao);
    
    people0.addContent(name);
    people0.addContent(nickname);
    people0.addContent(pass);
    people0.addContent(love);
    people0.addContent(city);
    people0.addContent(six);
    people0.addContent(jieshao);

    stu.addContent(people0);
            Document doc = new Document(stu);
            
            Format format = Format.getCompactFormat();
            format.setEncoding("gb2312"); //设置xml文件的字符为gb2312
            format.setIndent("    "); //设置xml文件的缩进为4个空格
            XMLOutputter XMLOut = new XMLOutputter(format);//在元素后换行，每一层元素缩排四格     
            try {
                XMLOut.output(doc, new FileOutputStream("E:\\book\\zhuce\\people-info.xml"));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            
    }
    
    public static void main(String[] args){
        WriteXML w=new WriteXML();
        w.wirteXml();
        w.insert();
System.out.println("aaaaaaaa");
        
    }
    }