使用Sax Parser跳过xml中的元素的最简单方法是什么？

Question

I've been looking around for an answer to this, but all of the SAX resources I find anywhere are a little bit less than I would want them to be. I am writing an android application for a restaurant which will give guests access to very long lists through an application rather than paging through a book. My xml looks something like this:

<bar>
    <liquor>
        <type>American Rye</type>
        <distillery>Sazerac<distillery>
        <bottling>18 Year</bottling>
        <place>Frankfort, KY</place>
        <proof>90</proof>
        <price>20<price>
    </liquor>

    <beer>
        <type>American Microbrew</type>
        <brewery>New Belgium</brewery>
        <bottling>La Folie Sour Brown 750ml</bottling>
        <place>Fort Collins, CO</place>
        <price>20</price>
    </beer>
</bar>

It was working well when I only had a couple hundred liquors. However, because I use certain element names, such as 'type' and 'price' twice, it is messing things up. Here is my parser:

public class BeerParser extends DefaultHandler {

private ArrayList<Beer> BeerL;
private boolean pastTheLiquor = false;

public ArrayList<Beer> getItems(String ArrayType){
    ArrayList<Beer> tmpItem = new ArrayList<Beer>();
    for (Beer beer : BeerL){
        if (beer.getType().equals(ArrayType)){
        tmpItem.add(beer);
            }
        }
    return tmpItem;
}


InputStream barXmlInputStream;

String tmpValue;


Beer beerTmp;



public BeerParser(InputStream barXmlInputStream) {



    this.barXmlInputStream = barXmlInputStream;

    BeerL = new ArrayList<Beer>();

    parseDocument();

    printDatas();

}

private void parseDocument() {



    SAXParserFactory factory = SAXParserFactory.newInstance();

    try {

        SAXParser parser = factory.newSAXParser();

        parser.parse(barXmlInputStream, this);



    } catch (ParserConfigurationException e) {

        System.out.println("ParserConfig error");

    } catch (SAXException e) {

        System.out.println("SAXException : xml not well formed");

    } catch (IOException e) {

        System.out.println("IO error");

    }

}

private void printDatas() {


    for (Beer tmpB : BeerL) {

        System.out.println(tmpB.toString());

    }


}

@Override

public void startElement(String s, String s1, String elementName, Attributes attributes) throws SAXException {


    if (elementName.equalsIgnoreCase("beer")) {

        pastTheLiquor = true;
        beerTmp = new Beer();



    }

}

@Override

public void endElement(String s, String s1, String element) throws SAXException {


    if (element.equals("beer")) {

            BeerL.add(beerTmp);

        }
    if (pastTheLiquor){
        if (element.equalsIgnoreCase("type")) {

            beerTmp.setType(tmpValue);

        }
        if (element.equalsIgnoreCase("brewery")) {

            beerTmp.setBrewery(tmpValue);

        }
        if (element.equalsIgnoreCase("bottling")) {

            beerTmp.setBottling(tmpValue);
            beerTmp.hasBottling = true;

        }

        if (element.equalsIgnoreCase("price")) {

            beerTmp.setPrice(tmpValue);

        }

        if (element.equalsIgnoreCase("place")) {

            beerTmp.setPlace(tmpValue);

        }
    }

}



@Override

public void characters(char[] ac, int i, int j) throws SAXException {

    tmpValue = new String(ac, i, j);

}

}

So, liquor was coming before beer, so, because the parser was seeing "type" before seeing "beer", it was trying to call the 'setType()' function of the Beer object beerTmp, which was never instantiated. I tried to use a boolean, which would wait until the parser saw the first instance of 'beer', but I am getting an empty list, which is really frustrating me, as the almost-identical parser that makes an array of liquors is working magnificently.

Is there an easy way to skip the liquors in the file? Am I on the right track with a boolean? Should I throw the SAX parser out the window and use something else? Thank you.

Answer 1

The sax parser invokes the callback for all the elements, if you don't want to consider some of them, just do a quick "return;". There is no way to filter them out before the parsing.

Is there an easy way to skip the liquors in the file? Am I on the right track with a boolean?

You can use Stack structure to park the data (push) that you'll need to consider later (pop).

SAX is definitely harder than other XML APIs to tame, for for some cases, it's the only option. So, don't give up with it; before or later you're gonna need it.

Answer 2

Following simplified virsion works. Note that

1) your xml have bugs, eg <type>American Rye</liquor>

2) equalsIgnoreCase is irrelevant since xml is case sensitive.

3) JAXB is the best for this job

public class BeerParser extends DefaultHandler {
    private List<Beer> list = new ArrayList<>();
    private Beer beer;
    private String element;

    public static void main(String[] args) throws Exception {
        SAXParserFactory factory = SAXParserFactory.newInstance();
        SAXParser parser = factory.newSAXParser();
        BeerParser bp = new BeerParser();
        parser.parse(new File("1.xml"), bp);
        System.out.println(bp.list);
    }

    @Override
    public void startElement(String s, String s1, String element, Attributes attributes) {
        if (element.equals("beer")) {
            beer = new Beer();
        }
        this.element = element;
    }

    @Override
    public void endElement(String s, String s1, String element) {
        if (element.equals("beer")) {
            list.add(beer);
            beer = null;
        }
    }

    @Override
    public void characters(char[] ac, int i, int j) {
        if (beer != null) {
            String value = new String(ac, i, j);
            if (element.equals("type")) {
                beer.setType(value);
            } else if (element.equals("brewery")) {
                beer.setBrewery(value);
            } else if (element.equals("bottling")) {
                beer.setBottling(value);
            } else if (element.equals("price")) {
                beer.setPrice(value);
            } else if (element.equals("place")) {
                beer.setPlace(value);
            }
        }
    }
}