運行沒問題，但xml裏的内容沒了，空了 什麽原因

package xml;

import java.io.FileOutputStream;

import java.io.OutputStreamWriter;

import java.io.Writer;

import org.dom4j.Document;

import org.dom4j.Element;

import org.dom4j.io.SAXReader;

public class dom4j02 {

public void readXml() {

String file="C:/Users/zhang/eclipse-workspace/xml/src/01xml.xml";

SAXReader reader = new SAXReader();

try {

Document document = reader.read(file);

Element root = document.getRootElement();

Element employee=root.addElement("employee");

// employee.addAttribute("no","3311");

Element name=employee.addElement("course-name");

name.setText("李四");

Writer writer=new OutputStreamWriter(new FileOutputStream(file),"UTF-8");//创建输出流

document.write(writer);

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

public static void main(String[] args) {

dom4j02 a = new dom4j02();

a.readXml();

}

}