Question

I am receving an XML file as an input, whose size can vary from a few KBs to a lot more. I am getting this file over a network. I need to extract a small number of nodes as per my use, so most of the document is pretty useless for me. I have no memory preferences, I just need speed.

Considering all this, I concluded :

1. Not using DOM here (due to possible huge size of doc , no CRUD requirement, and source being network)

2. No SAX as I only need to get a small subset of data.

3. StaX can be a way to go, but I am not sure if it is the fastest way.

4. JAXB came up as another option – but what sort of parser does it use ? I read it uses Xerces by default (which is what type – push or pull ?), although I can configure it for use with Stax or Woodstock as per this link

I am reading a lot, still confused with so many options ! Any help would be appreciated.

Thanks !

Edit : I want to add one more question here : What is wrong in using JAXB here ?

Answer 1

Fastest solution is by far a StAX parser, specially as you only need a specific subset of the XML file and you can easily ignore whatever isn’t really necessary using StAX, while you would receive the event anyway if you were using a SAX parser.

But it’s also a little bit more complicated than using SAX or DOM. One of these days I had to write a StAX parser for the following XML:

<?xml version="1.0"?>
<table>
    <row>
        <column>1</column>
        <column>Nome</column>
        <column>Sobrenome</column>
        <column>[e-mail]</column>
        <column></column>
        <column>2011-06-22 03:02:14.915</column>
        <column>2011-06-22 03:02:25.953</column>
        <column></column>
        <column></column>
    </row>
</table>    

Here’s how the final parser code looks like:

public class Parser {

private String[] files ;

public Parser(String ... files) {
    this.files = files;
}

private List<Inscrito> process() {

    List<Inscrito> inscritos = new ArrayList<Inscrito>();


    for ( String file : files ) {

        XMLInputFactory factory = XMLInputFactory.newFactory();

        try {

            String content = StringEscapeUtils.unescapeXml( FileUtils.readFileToString( new File(file) ) );

            XMLStreamReader parser = factory.createXMLStreamReader( new ByteArrayInputStream( content.getBytes() ) );

            String currentTag = null;
            int columnCount = 0;
            Inscrito inscrito = null;           

            while ( parser.hasNext() ) {

                int currentEvent = parser.next();

                switch ( currentEvent ) {
                case XMLStreamReader.START_ELEMENT: 

                    currentTag = parser.getLocalName();

                    if ( "row".equals( currentTag ) ) {
                        columnCount = 0;
                        inscrito = new Inscrito();                      
                    }

                    break;
                case XMLStreamReader.END_ELEMENT:

                    currentTag = parser.getLocalName();

                    if ( "row".equals( currentTag ) ) {
                        inscritos.add( inscrito );
                    }

                    if ( "column".equals( currentTag ) ) {
                        columnCount++;
                    }                   

                    break;
                case XMLStreamReader.CHARACTERS:

                    if ( "column".equals( currentTag ) ) {

                        String text = parser.getText().trim().replaceAll( "\n" , " "); 

                        switch( columnCount ) {
                        case 0:
                            inscrito.setId( Integer.valueOf( text ) );
                            break;
                        case 1:                         
                            inscrito.setFirstName( WordUtils.capitalizeFully( text ) );
                            break;
                        case 2:
                            inscrito.setLastName( WordUtils.capitalizeFully( text ) );
                            break;
                        case 3:
                            inscrito.setEmail( text );
                            break;
                        }

                    }

                    break;
                }

            }

            parser.close();

        } catch (Exception e) {
            throw new IllegalStateException(e);
        }           

    }

    Collections.sort(inscritos);

    return inscritos;

}

public Map<String,List<Inscrito>> parse() {

    List<Inscrito> inscritos = this.process();

    Map<String,List<Inscrito>> resultado = new LinkedHashMap<String, List<Inscrito>>();

    for ( Inscrito i : inscritos ) {

        List<Inscrito> lista = resultado.get( i.getInicial() );

        if ( lista == null ) {
            lista = new ArrayList<Inscrito>();
            resultado.put( i.getInicial(), lista );
        }

        lista.add( i );

    }

    return resultado;
}

}

The code itself is in portuguese but it should be straightforward for you to understand what it is, here’s the repo on github.