dom4j生成xml，中文乱码，怎么解决

package com.zjm.xml;import java.io.File;import java.io.FileWriter;import org.dom4j.Document;import org.dom4j.DocumentHelper;import org.dom4j.Element;import org.dom4j.io.OutputFormat;import org.dom4j.io.XMLWriter;public class createXML {    /**     * @param args     */    public static void main(String[] args) {        // TODO Auto-generated method stub        createXML xml = new createXML();        xml.create();    }        public boolean create() {        boolean flag = false;        Document document = null;        //文档        Element books = null;            //根节点        Element book = null;            //book节点        Element text = null;            //text节点        OutputFormat format = null;        XMLWriter writer = null;                try {            document = DocumentHelper.createDocument();            books = document.addElement("books");            books.addComment("注释");                        book = books.addElement("book");            book.addAttribute("name", "book1");            book.addAttribute("show", "true");            text = book.addElement("text");            text.setText("text1");                        book = books.addElement("book");            book.addAttribute("name", "book2");            book.addAttribute("show", "false");            text = book.addElement("text");            text.setText("text2");                        format = OutputFormat.createPrettyPrint();            format.setEncoding("GBK");            //format.setEncoding("UTF-8");    //用utf-8也不行                        System.out.println(document.asXML());                        writer = new XMLWriter(new FileWriter(new File("E://mytext.xml")), format);            writer.write(document);            writer.close();                        flag = true;                        return flag;        }        catch(Exception e) {            e.printStackTrace();        }        return flag;    }}

<?xml version="1.0" encoding="GBK"?><books>  <!--??-->            <book name="book1" show="true">    <text>text1</text>  </book>  <book name="book2" show="false">    <text>text2</text>  </book></books>