Although DOM is a read-write API in memory, it’s sorely lacking when it comes to moving its in-memory data structure back out onto a disk, a network socket, or some other stream. Eventually, this omission will be rectified in DOM Level 3. In the meantime, you have the choice of either using implementation-specific serialization classes or using JAXP. The implementation-specific serialization classes generally provide more customization and features, but JAXP is enough for basic uses.
JAXP doesn’t include a serialization package, but you can hack basic output through the javax.xml.transform package by conveniently “forgetting” to install a transform. :-) The pattern is the same as parsing a document with JAXP. The basic steps are as follows:
Use the static TransformerFactory.newInstance() factory method to return a javax.xml.transform.TransformerFactory object.
Use the newTransformer() method of this TransformerFactory object to return an implementation-specific instance of the abstract javax.xml.transform.Transformer class.
Construct a new javax.xml.transform.dom.DOMSource object from your DOM Document object.
Construct a new javax.xml.transform.stream.StreamResult object connected to the OutputStream you want to write the document onto.
Pass both the source and the result objects to the transform() method of the Transformer object created in step 2.
We can use this procedure to write a simple driver program for Example 9.12. Example 9.14 first uses JAXP to build a DOM Document object from a URL, then passes this object to the Restructurer.processNode() method, and finally serializes the whole document onto System.out.
Example 9.14. Using JAXP to both read and write an XML document
import javax.xml.parsers.*; // JAXP
import javax.xml.transform.*; // JAXP
import javax.xml.transform.dom.DOMSource; // JAXP
import javax.xml.transform.stream.StreamResult; // JAXP
import org.xml.sax.SAXException;
import org.w3c.dom.Document;
import java.io.IOException;
public class RestructureDriver {
public static void main(String[] args) {
if (args.length <= 0) {
System.out.println("Usage: java RestructureDriver URL");
return;
}
String url = args[0];
try {
// Find a parser
DocumentBuilderFactory factory
= DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder parser = factory.newDocumentBuilder();
// Read the document
Document document = parser.parse(url);
// Modify the document
Restructurer.processNode(document);
// Write it out again
TransformerFactory xformFactory
= TransformerFactory.newInstance();
Transformer idTransform = xformFactory.newTransformer();
Source input = new DOMSource(document);
Result output = new StreamResult(System.out);
idTransform.transform(input, output);
}
catch (SAXException e) {
System.out.println(url + " is not well-formed.");
}
catch (IOException e) {
System.out.println(
"Due to an IOException, the parser could not read " + url
);
}
catch (FactoryConfigurationError e) {
System.out.println("Could not locate a factory class");
}
catch (ParserConfigurationException e) {
System.out.println("Could not locate a JAXP parser");
}
catch (TransformerConfigurationException e) {
System.out.println("This DOM does not support transforms.");
}
catch (TransformerException e) {
System.out.println("Transform failed.");
}
}
}
You’ll learn how to actually use these classes for their intended purposes of XSLT transforms in the final chapter.
| Copyright 2001, 2002 Elliotte Rusty Harold | elharo@metalab.unc.edu | Last Modified May 26, 2002 |
| Up To Cafe con Leche |