Reading Transformer result line by line (Java)

I'm using Transformer to prettify and to insert indentation to an XML which is originally one big line. Here is my code:

BufferedWriter br = null;
Source xmlInput = new StreamSource(inputSR);
StringWriter stringWriter = new StringWriter();
StreamResult xmlOutput = new StreamResult(stringWriter);
TransformerFactory transformerFactory = TransformerFactory.newInstance();
transformerFactory.setAttribute("indent-number", 2);
Transformer transformer = transformerFactory.newTransformer(); 
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.transform(xmlInput, xmlOutput);

How can I write the xmlOutput to a file, line by line (without loading the whole string to the memory)?