创建xml文档时，如何修改其默认编码utf-8为gb2312

因为XML文档中有中文字符，是否是因为编码不对造成的呢？该如何解决呢？请教！public void createXMLDocument(){
    Document doc = null;
    Element people=null,person=null,name=null,age=null,sex=null;
    try{
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
      DocumentBuilder db = dbf.newDocumentBuilder();
      doc = db.newDocument();      if(doc != null){
        people = doc.createElement("People");        person = doc.createElement("Person");
        person.setAttribute("id","1");
        people.appendChild(person);        name = doc.createElement("Name");
        name.appendChild(doc.createTextNode("张三"));
        person.appendChild(name);        age = doc.createElement("Age");
        age.appendChild(doc.createTextNode("20"));
        person.appendChild(age);        sex = doc.createElement("Sex");
        sex.appendChild(doc.createTextNode("男"));
        person.appendChild(sex);        doc.appendChild(people);        ((XmlDocument)doc).write(System.out);
      }
    }
    catch(Exception e){
      System.out.println(e.toString());
    }
  }