Partial Unmarshalling of an XML using JAXB to skip some xmlElement - xml-parsing

Question

I want to unmarshal an XML file to java object using JAXB. The XML file is very large and contains some nodes which I want to skip in some cases to improve performance as these elements are non editable by client java program.
A sample XML is as follows:
<Example id="10" date="1970-01-01" version="1.0">
<Properties>...</Properties>
<Summary>...</Summary>
<RawData>
<Document id="1">...</Document>
<Document id="2">...</Document>
<Document id="3">...</Document>
------
------
</RawData>
<Location></Location>
<Title></Title>
----- // more elements
</Example>
I have two use cases:
unmarshal into Example object which contains Properties, Summaries, RawData etc. without skipping any RawData. (already done this part)
unmarshal into Example object which exclude RawData. Elements nested in RawData is very large so do not want to read this in this use case.
Now I want to unmarshal the XML such that RawData can be skipped. I have tried the technique provided at this link.
Using technique provided in above link also skips all elements which come after RawData.

Answer 1

I have fixed the issue with XMLEventReader with following code:
public class PartialXmlEventReader implements XMLEventReader {
private final XMLEventReader reader;
private final QName qName;
private boolean skip = false;
public PartialXmlEventReader(final XMLEventReader reader, final QName element) {
this.reader = reader;
this.qName = element;
}
#Override
public String getElementText() throws XMLStreamException {
return reader.getElementText();
}
#Override
public Object getProperty(final String name) throws IllegalArgumentException {
return reader.getProperty(name);
}
#Override
public boolean hasNext() {
return reader.hasNext();
}
#Override
public XMLEvent nextEvent() throws XMLStreamException {
while (isEof(reader.peek())) {
reader.nextEvent();
}
return reader.nextEvent();
}
#Override
public XMLEvent nextTag() throws XMLStreamException {
return reader.nextTag();
}
#Override
public XMLEvent peek() throws XMLStreamException {
return reader.peek();
}
#Override
public Object next() {
return reader.next();
}
#Override
public void remove() {
reader.remove();
}
#Override
public void close() throws XMLStreamException {
reader.close();
}
private boolean isEof(final XMLEvent e) {
boolean returnValue = skip;
switch (e.getEventType()) {
case XMLStreamConstants.START_ELEMENT:
final StartElement se = (StartElement) e;
if (se.getName().equals(qName)) {
skip = true;
returnValue = true;
}
break;
case XMLStreamConstants.END_ELEMENT:
final EndElement ee = (EndElement) e;
if (ee.getName().equals(qName)) {
skip = false;
}
break;
}
return returnValue;
}
}
While Unmarshalling just pass this eventReader to the unmarshal method
final JAXBContext context = JAXBContext.newInstance(classes);
final Unmarshaller um = context.createUnmarshaller();
Reader reader = null;
try {
reader = new BufferedReader(new FileReader(xmlFile));
final QName qName = new QName("RawData");
final XMLInputFactory xif = XMLInputFactory.newInstance();
final XMLEventReader xmlEventReader = xif.createXMLEventReader(reader);
final Example example =
(Example) um.unmarshal(new PartialXmlEventReader(xmlEventReader, qName));
}
} finally {
IOUtils.closeQuietly(reader);
}

Answer 2

I hope this would help
try {
// First create a new XMLInputFactory
XMLInputFactory inputFactory = XMLInputFactory.newInstance();
// Setup a new eventReader
InputStream in = new FileInputStream("myXml");
XMLEventReader eventReader = inputFactory.createXMLEventReader(in);
// Read the XML document
Example example = null;
while (eventReader.hasNext()) {
XMLEvent event = eventReader.nextEvent();
if (event.isStartElement()) {
StartElement startElement = event.asStartElement();
// If we have a example element we create a new example
if (startElement.getName().getLocalPart().equals("Example")) {
example = new Example();
// We read the attributes from this tag and add the date
// and id attribute to our object
Iterator<Attribute> attributes = startElement
.getAttributes();
while (attributes.hasNext()) {
Attribute attribute = attributes.next();
if (attribute.getName().toString().equals("date")) {
example.setDate(attribute.getValue());
} else if (attribute.getName().toString().equals("id")) {
example.setId(attribute.getValue());
}
}
}
//get the Properties tag and add to object example
if (event.isStartElement()) {
if (event.asStartElement().getName().getLocalPart()
.equals("Properties")) {
event = eventReader.nextEvent();
example.setProperites(event.asCharacters().getData());
continue;
}
}
//get the Summary tag and add to object example
if (event.asStartElement().getName().getLocalPart()
.equals("Summary")) {
event = eventReader.nextEvent();
example.setSummary(event.asCharacters().getData());
continue;
}
// when you encounter the Rawdata tag just continue
//without adding it to the object created
if (event.asStartElement().getName().getLocalPart()
.equals("Rawdata")) {
event = eventReader.nextEvent();
// don't do anything
continue;
}
//get the location tag and add to object example
if (event.asStartElement().getName().getLocalPart()
.equals("Location")) {
event = eventReader.nextEvent();
example.setLocation(event.asCharacters().getData());
continue;
}
// read and add other elements that can be added
}
// If we reach the end of an example element/tag i.e closing tag
if (event.isEndElement()) {
EndElement endElement = event.asEndElement();
if (endElement.getName().getLocalPart().equals("Example")) {
//do something
}
}
}
} catch (FileNotFoundException | XMLStreamException e) {
}