Parsing large XML documents in JAVA

Question

I have the following problem:

I\'ve got an XML file (approx 1GB), and have to iterate up and down (i.e. not sequential; one after the other) in order to get the req

Answer 1

SAX (Simple API for XML) will help you here.

Unlike the DOM parser, the SAX parser does not create an in-memory representation of the XML document and so is faster and uses less memory. Instead, the SAX parser informs clients of the XML document structure by invoking callbacks, that is, by invoking methods on a org.xml.sax.helpers.DefaultHandler instance provided to the parser.

Here is an example implementation:

SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
DefaultHandler handler = new MyHandler();
parser.parse("file.xml", handler);

Where in MyHandler you define the actions to be taken when events like start/end of document/element are generated.

class MyHandler extends DefaultHandler {

    @Override
    public void startDocument() throws SAXException {
    }

    @Override
    public void endDocument() throws SAXException {
    }

    @Override
    public void startElement(String uri, String localName, String qName,
            Attributes attributes) throws SAXException {
    }

    @Override
    public void endElement(String uri, String localName, String qName)
            throws SAXException {
    }

    // To take specific actions for each chunk of character data (such as
    // adding the data to a node or buffer, or printing it to a file).
    @Override
    public void characters(char ch[], int start, int length)
            throws SAXException {
    }

}