java - How to strip whitespace-only text nodes from a DOM before serialization?

Question

I have some Java (5.0) code that constructs a DOM from various (cached) data sources, then removes certain element nodes that are not required, then serializes the result into an XML string using:

// Serialize DOM back into a string
Writer out = new StringWriter();
Transformer tf = TransformerFactory.newInstance().newTransformer();
tf.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
tf.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
tf.setOutputProperty(OutputKeys.INDENT, "no");
tf.transform(new DOMSource(doc), new StreamResult(out));
return out.toString();

However, since I'm removing several element nodes, I end up with a lot of extra whitespace in the final serialized document.

Is there a simple way to remove/collapse the extraneous whitespace from the DOM before (or while) it's serialized into a String?

Answer 1

You can find empty text nodes using XPath, then remove them programmatically like so:

XPathFactory xpathFactory = XPathFactory.newInstance();
// XPath to find empty text nodes.
XPathExpression xpathExp = xpathFactory.newXPath().compile(
        "//text()[normalize-space(.) = '']");  
NodeList emptyTextNodes = (NodeList) 
        xpathExp.evaluate(doc, XPathConstants.NODESET);

// Remove each empty text node from document.
for (int i = 0; i < emptyTextNodes.getLength(); i++) {
    Node emptyTextNode = emptyTextNodes.item(i);
    emptyTextNode.getParentNode().removeChild(emptyTextNode);
}

This approach might be useful if you want more control over node removal than is easily achieved with an XSL template.