Using XPath to create nodes

Question

Hi,
Obviously the main use of XPath is to query the state of an XML document... the equivalent to a "select" statement in SQL.
DOM4J has methods that allow you to use XPath as the equivalent to "insert" statements in SQL. You can specify an XPath like "/Hello/World/Value = 3" and apply this XPath to an XML document so that it creates something like this for you:
<Hello>
<World>
<Value>3</Value>
</World>
</Hello>
This is actually very useful for an investment banking application that I'm working on.
The problem with DOM4J is that it doesn't handle attributes or conditionals well. If you specify
/Hello[@name=2]/World = 3
I would expect
<Hello name=2>
<World>3</World>
</Hello>
to be produced. Instead, it produces
<Hello[@name=2]>
<World>3</World>
</Hello>
These are all simple examples. What I'm doing in real life is using XPath to insert nodes into a complicated XML document that already has a lot of structure. I'm only adding one or two elements to big documents.
Is there anything at all like this available in the JDK 1.5 release. I've had a good look, and XPath looks like it's only for queries. Is this correct?

Answer 1

I think this might do what you need...
// Create a dummy XML document
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
InputStream bais = new ByteArrayInputStream("<test><e1/></test>".getBytes());       
Document doc = db.parse(bais);
// Define the XPath expression to "select" the parent element in the document       
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression xpathExpression = xpath.compile("/test/e1");    
// Select the parent node (should probably chuck an ex if not present)       
Node node = (Node) xpathExpression.evaluate(doc, XPathConstants.NODE);
// Create and append the child element
node.appendChild(doc.createElement("newElement"));
// Convert the Document into a string
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(baos);
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
transformer.transform(source, result);
// <?xml version="1.0" encoding="UTF-8"?><test><e1><newElement/></e1></test>
System.out.println(baos.toString());