Parsing xml with DOM, DOCTYPE gets erased

how come dom with java erases doctype when editing xml ?

got this xml file :

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE map[ <!ELEMENT map (station*) >
                <!ATTLIST station  id   ID    #REQUIRED> ]>
<favoris>
<station id="5">test1</station>
<station id="6">test1</station>
<station id="8">test1</station>
</favoris> 

my function is very basic :

public static void EditStationName(int id, InputStream is, String path, String name) throws ParserConfigurationException, SAXException, IOException, TransformerFactoryConfigurationError, TransformerException{
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

    DocumentBuilder builder = factory.newDocumentBuilder();
    Document dom = builder.parse(is);

    Element e = dom. getElementById(String.valueOf(id));
    e.setTextContent(name);
    // Write the DOM document to the file
    Transformer xformer = TransformerFactory.newInstance().newTransformer();
    FileOutputStream fos = new FileOutputStream(path);
    Result result = new StreamResult(fos);  
    Source source = new DOMSource(dom);


        xformer.setOutputProperty(
                OutputKeys.STANDALONE,"yes"     
                );

    xformer.transform(source, result);
}

it's working but the doctype gets erased ! and I just got the whole document but without the doctype part, which is important for me because it allows me to retrieve by id ! how can we keep the doctype ? why does it erase it? I tried many solution with outputkeys for example or omImpl.createDocumentType but none of these worked...

thank you !