//写入XML
    private void writeXML(Document doc) {
        OutputFormat format = OutputFormat.createPrettyPrint();
        format.setEncoding("UTF-8");
        try {
            XMLWriter writer = new XMLWriter(new FileOutputStream("C:\\info.xml"), format);
            writer.write(doc);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    //添加管理员
    public void insert(Student student) throws Exception {
        Document doc = this.readXML();

        Element root = doc.getRootElement();
        Element studentElement = root.addElement("student");

        Element studentNameElement = studentElement .addElement("name");
        usernameElement.addText(student.getStudentName());
        
        Element passwordElement = studentElement .addElement("password");
        passwordElement.addText(student.getPassword());

                ....
        this.writeXML(doc);
    }
    }

------解决方案--------------------
Java code
    //读取XML
    private Document readXML() throws Exception {

        SAXReader reader = new SAXReader();

        Document doc = reader.read(new File"C:\\info.xml"));
        return doc;

    }

------解决方案--------------------
SAX 不能用于添加节点