java - Can JAXB parse large XML files in chunks

Question

I need to parse potentially large XML files, of which the schema is already provided to me in several XSD files, so XML binding is highly favored. I'd like to know if I can use JAXB to parse the file in chunks and if so, how.

Answer 1

Because code matters, here is a PartialUnmarshaller who reads a big file into chunks. It can be used that way new PartialUnmarshaller<YourClass>(stream, YourClass.class)

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.*;
import java.io.InputStream;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import static javax.xml.stream.XMLStreamConstants.*;

public class PartialUnmarshaller<T> {
    XMLStreamReader reader;
    Class<T> clazz;
    Unmarshaller unmarshaller;

    public PartialUnmarshaller(InputStream stream, Class<T> clazz) throws XMLStreamException, FactoryConfigurationError, JAXBException {
        this.clazz = clazz;
        this.unmarshaller = JAXBContext.newInstance(clazz).createUnmarshaller();
        this.reader = XMLInputFactory.newInstance().createXMLStreamReader(stream);

        /* ignore headers */
        skipElements(START_DOCUMENT, DTD);
        /* ignore root element */
        reader.nextTag();
        /* if there's no tag, ignore root element's end */
        skipElements(END_ELEMENT);
    }

    public T next() throws XMLStreamException, JAXBException {
        if (!hasNext())
            throw new NoSuchElementException();

        T value = unmarshaller.unmarshal(reader, clazz).getValue();

        skipElements(CHARACTERS, END_ELEMENT);
        return value;
    }

    public boolean hasNext() throws XMLStreamException {
        return reader.hasNext();
    }

    public void close() throws XMLStreamException {
        reader.close();
    }

    void skipElements(int... elements) throws XMLStreamException {
        int eventType = reader.getEventType();

        List<Integer> types = asList(elements);
        while (types.contains(eventType))
            eventType = reader.next();
    }
}