How to stream XML data using XOM?

Question

Say I want to output a huge set of search results, as XML, into a PrintWriter or an OutputStream, using XOM. The resulting XML would look like this:

Answer 1

I ran in to the same issue, but found it's pretty simple to do what you mentioned as an option and subclass Serializer as follows:

public class StreamSerializer extends Serializer {

    public StreamSerializer(OutputStream out) {
        super(out);
    }

    @Override
    public void write(Element element) throws IOException {
        super.write(element);
    }

    @Override
    public void writeXMLDeclaration() throws IOException {
        super.writeXMLDeclaration();
    }

    @Override
    public void writeEndTag(Element element) throws IOException {
        super.writeEndTag(element);
    }

    @Override
    public void writeStartTag(Element element) throws IOException {
        super.writeStartTag(element);
    }

}

Then you can still take advantage of the various XOM config like setIdent, etc. but use it like this:

Element rootElement = new Element("resultset");
StreamSerializer serializer = new StreamSerializer(out);
serializer.setIndent(4);
serializer.writeXMLDeclaration();
serializer.writeStartTag(rootElement);
while(hasNextElement()) {
    serializer.write(nextElement());
}
serializer.writeEndTag(rootElement);
serializer.flush();

Answer 2

As far as I know, XOM doesn't support streaming directly.

What I used when I wanted to stream my XML documents was NUX, which has Streaming XML Serializer, similar to standard Serializer class in XOM. NUX is compatible with XOM. I downloaded NUX sources, extracted few NUX classes (StreamingSerializer interface, StreamingXMLSerializer -- which works for XOM documents, StreamingVerifier and NamespacesInScope), put them into my project, and it works like a charm. Too bad this isn't directly in XOM :-(

NUX is very nice companion to XOM: http://acs.lbl.gov/software/nux/, working mirror download: nux-1.6.tar.gz

Link to API: http://acs.lbl.gov/software/nux/api/nux/xom/io/StreamingSerializer.html

Here is sample code (methods are called in order: start(), n*nextResult(), finish(), serializer is StreamingXMLSerializer from NUX):

void start() {
    serializer.writeXMLDeclaration();

    Element root = new Element("response");
    root.addAttribute(new Attribute("found", Integer.toString(123)));
    root.addAttribute(new Attribute("count", Integer.toString(542)));

    serializer.writeStartTag(root);

    serializer.flush();
}

void nextResult(Result result) {
    Element element = result.createXMLRepresentation();
    serializer.write(element);
    serializer.flush();
}

void finish() {
    serializer.writeEndTag();
    serializer.flush();
}