程序代码：

public static void write() {  
        try {  
            // 创建一个xml文档  
            Document doc = DocumentHelper.createDocument();             
            Element root = doc.addElement("root");  //创建一个根元素
            root.addAttribute("id", "1");  //为根元素添加一个属性
            
            Element student = root.addElement("student");  //root根元素添加一个子元素student
            student.addAttribute("id", "2");  //为student添加属性
            
             Element student1 = root.addElement("student");  //root根元素添加一个子元素student
             student1.addAttribute("id","3");//为student添加属性
              
            File file = new File("src/dom4j-modify.xml");  
            if (file.exists()) {  
                file.delete();  
            }  
            file.createNewFile();  
            XMLWriter out = new XMLWriter(new FileWriter(file));  
            out.write(doc);  
            out.flush();  
            out.close();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }