I thought I understood XML ........

Question

Hi, Can anyone help me out here. Although I understand about XML and have written al lot of stuff to process XML, it was in a language that came out of a company based in Redmond :).
I take one look at the Java stuff and get very confused.
I want to export the Preferences of an application to a file, which using is easily done using the standard package and this produces a "stream". Before I send the contents to a file I want to delete some of the nodes in the preferences as they are specific to that instance of the application. I would therefore like to edit the XML before it is written. I would normally make a XML Document object from the XML in the stream and make my changes to that, finally sending the content of the document to a file. Easy enough I thinks, and it is in the other language.
In java I try to make a document with a DocumentBuilderFactory and DocumentBuilder and when I try to run the program I get an UnknownHostException because the computer involved cannot connect to the internet and download the DTD specified in the XML Stream. The offending line is part of the exported XML cannot be remove as I will also want it in the final output for when it is imported again.
I have seen all sorts of articles about different packages, parsers and the like and I am now totally confused. I did try making a custom entity resolver but that didnt work either. I tried to use the SAX parser but could not work out how to make that give me a document.I'm not even sure this is the right thing to do.
Can someone point me to where this might be explained in simple terms because I really am totally confused now.
Thanks
Terry

Answer 1

Ok first, sorry if I was appearing to "have a sly go" at Java, I was actually trying to infer that it was my lack of knowledge and inability to get my head around this rather than anything "wrong" with java. I spent 15 years learning the other stuff and so if I didn't understand that side of things then I should have given up and become a road sweeper. I've only spent 3 months on this in a serious way.
Anyway that said I am still confused by all the different parsers and things and there are lots of examples out there but none I have found really explain why I would want to use a particular parser or what I can do with them etc.
Ok back to my original problem, this is the code and its just a little piece of prototype so please ignore any redundant imports or improper exception handling and that sort of error,
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package xxxx.xxxxxxx.xxxx.xxx;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.prefs.BackingStoreException;
import java.util.prefs.Preferences;
import javax.xml.parsers.ParserConfigurationException;
import org.xml.sax.SAXException;
public class GlobalData {
    private Preferences prefs;
    public void setPreference() throws SAXException, ParserConfigurationException, IOException {
        prefs = Preferences.systemNodeForPackage(GlobalData.class);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        //OutputStream out = System.out;
        try {
            // prefs.exportSubtree(out);
            prefs.exportSubtree(baos);
        } catch (IOException ex) {
            Logger.getLogger(GlobalData.class.getName()).log(Level.SEVERE, null, ex);
        } catch (BackingStoreException ex) {
            Logger.getLogger(GlobalData.class.getName()).log(Level.SEVERE, null, ex);
        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setValidating(false);
        DocumentBuilder builder = factory.newDocumentBuilder();
        EntityResolver customEntityResolver = new DummyEntityResolver();
        builder.setEntityResolver(customEntityResolver);
        Document xDoc = builder.parse(bais);
        //System.out.println(xDoc.toString());
    public static void main(String[] args) {
        GlobalData test = new GlobalData();
        try {
            test.setPreference();
        } catch (ParserConfigurationException ex) {
            Logger.getLogger(GlobalData.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SAXException ex) {
            Logger.getLogger(GlobalData.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(GlobalData.class.getName()).log(Level.SEVERE, null, ex);
public class DummyEntityResolver implements EntityResolver{
    public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {
        return null;
}I thought I got it right but obviously not.
When it hits the parse then I get the UnknownHostException just the same as without the custom EntityResolver.
If you can help I would be grateful.
Thanks
Terry