updating xml from java

I have a small problem with writing new data in an already existing xml file from java. It is my first try with xml files, so I'm not too familiar with them and I don't really understand why is this happening. Matter of fact is that I call the function which should update the file, but nothing happens with it.

Here is the syntax of my xml file:

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
 <book genre="COOKING">
    <title>Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <quantity>5</quantity>
    <price>30.00</price>
 </book>
 <book genre="CHILDREN">
    <title>Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <quantity>7</quantity>
    <price>29.99</price>
 </book>
 <book genre="WEB">
    <title>Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <quantity>15</quantity>
    <price>39.95</price>
 </book>
</bookstore>

I tried the solution from here: How do I append a node to an existing XML file in java, accompanied with this one: http://ift.tt/1cGspWw, but it's still not modifying anything.

Here is my code:

public void createBook(String title, String author, int year, String genre, int quantity, int price)
{
    try 
    {
        File xmlBookFile = new File(xmlBook);
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        Document doc = documentBuilder.parse(xmlBookFile);
        doc.getDocumentElement().normalize();
        Element rootElement = doc.getDocumentElement();
        Node bookNode = createNode(doc);
        rootElement.appendChild(bookNode);
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(doc);
        StreamResult result = new StreamResult(new File(xmlBook));
        transformer.transform(source, result);
    }
    catch (Exception e) 
    {
    e.printStackTrace();
    }
}

public Node createNode(Document doc)
{
    Element bookElement = doc.createElement("book");
    Attr genreAttribute = doc.createAttribute("genre");
    genreAttribute.setValue(genre);
    Element titleElement = doc.createElement("title");
    titleElement.appendChild(doc.createTextNode(title));
    Element authorElement = doc.createElement("author");
    authorElement.appendChild(doc.createTextNode(author));
    Element yearElement = doc.createElement("year");
    yearElement.appendChild(doc.createTextNode(Integer.toString(year)));
    Element quantityElement = doc.createElement("quantity");
    quantityElement.appendChild(doc.createTextNode(Integer.toString(quantity)));
    Element priceElement = doc.createElement("price");
    priceElement.appendChild(doc.createTextNode(Integer.toString(price)));
    bookElement.setAttributeNode(genreAttribute);
    bookElement.appendChild(titleElement);
    bookElement.appendChild(authorElement);
    bookElement.appendChild(yearElement);
    bookElement.appendChild(quantityElement);
    bookElement.appendChild(priceElement);
    return bookElement;
}

I would appreciate every bit of help why isn't this updating my file and what do I do wrong. Thank you!