Set XmlEncoding to Dom Document in Java

Question

I need set the XmlEncoding (UTF-8) in a Dom Document object without use a Transformer with his "setOutputProperty(OutputKeys.ENCODING, "UTF-8")" method.

I don't want obtain the XML string using the Transform object because I am using a Xades XMLSignature library which uses a Document object to sign.

The problem is that for a Dom Document created as follow, his getXmlEncoding() method returns null.

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder = factory.newDocumentBuilder();     
Document document = builder.newDocument();
document.getXmlEncoding();  //Returns null

But after apply the following code, the XmlEncoding methoth of the new DOM Document returns UTF-8 (requeriment for my xades library). It's because the transformation process has added the encoding somehow. For performance reasons I want to avoid to execute this code.

TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");        

DOMSource source = new DOMSource(document);
Writer writer = new StringWriter();
StreamResult result = new StreamResult(writer);
transformer.transform(source, result);

String xml = writer.toString(); 
InputStream stream = new ByteArrayInputStream(xml.getBytes(StandardCharsets.UTF_8));

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();    
dbf.setNamespaceAware(true);            
Document newDocument = dbf.newDocumentBuilder().parse(inputStream);

newDocument.getXmlEncoding(); //returns "UTF-8"

How I can create the Dom Document with the prolog information?

Answer 1

You could try using Apache Axiom's DOM implementation. It implements both the DOM API and Axiom's own API, which actually allows setting the XML encoding. Simply add axiom-dom to your project and use the following instruction to get a DocumentBuilderFactory:

DocumentBuilderFactory factory = ((DOMMetaFactory)OMAbstractFactory.getMetaFactory(OMAbstractFactory.FEATURE_DOM)).newDocumentBuilderFactory();

You can then set the XML encoding on a document as follows:

((OMDocument)document).setXMLEncoding("utf-8");

The rest of your code remains unchanged and can continue using the DOM API.