Processing Xml With Java - A Guide To Sax, Dom, Jdom, Jaxp, And Trax

JAXP Serialization

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 DOM3. In the meantime, you have the choice of using either implementation-specific serialization classes or JAXP. The implementation-specific serialization classes generally provide more customization and features, but JAXP is sufficient 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:

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 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 transformation in Chapter 17.