线程“主” org.w3c.dom.DOM中的异常：HIERARCHY_REQUEST_ERR：试图在不允许的节点上插入节点

Question

我正在尝试使用DOM从Java创建xml文档。但是我不确定我在哪里。我在线程“主” org.w3c.dom.DOMException中收到错误Exception：HIERARCHY_REQUEST_ERR：试图在不允许的节点上插入节点。请尝试解决此问题。我需要创建单独的xml文件，并在该文件中写入我的预期输出

Mainclass
    public static void main(String[] args) {
    Scanner obj = new Scanner(System.in);

    int unit=0;
    ArrayList<Books> bookslist = new ArrayList<Books>();

    System.out.println("Enter the amount of books need to add");
    unit = obj.nextInt();
    Books books = new Books();
    for(int i=0;i<unit;i++)
    {
        System.out.println("enter the book name");
        books.setName(obj.next());
        System.out.println("enter the author name");
        books.setAuthor(obj.next());
        System.out.println("enter the book price");
        books.setPrice(obj.nextFloat());

        bookslist.add(books);
    }
    CreateXml createxml = new CreateXml(bookslist,unit);
}

}

CreateXml.java

public CreateXml(ArrayList<Books> bookslist, int unit) {

    try{
         DocumentBuilderFactory documentFactory = DocumentBuilderFactory.newInstance();  
         DocumentBuilder documentBuilder = documentFactory.newDocumentBuilder();
         Document document = documentBuilder.newDocument();

          for(int i=0;i<unit;i++)
          {
              Element rootElement = document.createElement("BookList");
              document.appendChild(rootElement); 
          Element book= document.createElement("Book");
          rootElement.appendChild(book);

          Element bookname=document.createElement("Name");
          bookname.appendChild(document.createTextNode(bookslist.get(i).getName()));
          book.appendChild(bookname);


          Element authorname = document.createElement("Author");
          authorname.appendChild(document.createTextNode(bookslist.get(i).getAuthor()));
          book.appendChild(authorname);



          Attr attribute = document.createAttribute("Price");
          attribute.setValue(String.valueOf(bookslist.get(i).getPrice()));
          book.appendChild(attribute);
          }
          TransformerFactory transformerfactory = TransformerFactory.newInstance();
          Transformer transformer = transformerfactory.newTransformer();
          DOMSource domSource = new DOMSource(document);
          System.out.println(document);
          StreamResult streamResult = new StreamResult(new File("createdFiles/createFile.xml"));  

                   transformer.transform(domSource, streamResult);               
    }

     catch (ParserConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (TransformerConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (TransformerException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


 I'm expecting this output 
<BookList>
<Book>
<Name>vdg</Name>
<Price>89.26</Price>
<Author>bfkj</Author>
</Book>
<Book>
<Name>vdg</Name>
<Price>89.26</Price>
<Author>bfkj</Author>
</Book>
</BookList>