Searching with SAX in xml

[Sebastian Green]

I want to search an xml-file using the SAX-parser. Like, show all nodes where the personid-node equals 001. Im having a hard time understanding XML and SAX in generall. Can anyone help me, point me in tha right direction? I have tried to use the ranchs wiki faq tutorial. But it didnt help so much...

[Hari Vignesh Padmanaban]

look at this
http://java.sun.com/xml/jaxp/dist/1.1/docs/tutorial/sax/index.html
hope this helps

[Lasse Koskela]

It might be a lot easier to start with DOM instead of SAX.
With DOM, you get an object tree which you can iterate with for loops etc. and pick the nodes that match into, say, an ArrayList.

[Sebastian Green]

Perhaps I should start with the DOM but the task rquiers using SAX. And the Sun-Tutorial is very long, Im looking for something shorter. I found something at the The Java Developers Almanac (http://www.javaalmanac.com/egs/javax.xml.parsers/BasicSax.html) but its only parse the xml-file. I want to the parser to print out every childnode to every node called <person>.

[Anonymous]

Even better, use of XPath (as in XSLT) would be better (with Xalan for instance).
The XPath expression for returning all the person whose id nodes equals to 1 would look something like:

String xPath = "//person[id=1]";

For instance, in the following xml document there are a number of person nodes:

<?xml version="1.0"?>
<sample>
    <person>
        <id>002</id>
        <name>Smith</name>
    </person>
    <person>
        <id>001</id>
        <name>Johnson</name>
    </person>
</sample>

The following code will display the person with id 001:

import org.apache.xpath.XPathAPI;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.SAXException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.IOException;
import java.io.InputStream;
public class XPathSample {
    public static void main(String[] args) throws ParserConfigurationException, IOException, SAXException, TransformerException {
        InputStream is = XPathSample.class.getResourceAsStream("sample.xml");
        DocumentBuilder documentBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document document = documentBuilder.parse(is);
        String xPathExpr = "//person[id='001']";
        Node node = XPathAPI.selectSingleNode(document, xPathExpr);
        if (node != null)
            printNode(node);
    }
    private static void printNode(Node node) throws TransformerException {
        Transformer transformer = TransformerFactory.newInstance().newTransformer();
        transformer.transform(new DOMSource(node), new StreamResult(System.out));
        System.out.println();
    }
}

Cheers

[Anonymous]

Sebastian,
If you'd like to use Sax events, it's another story as no document tree is available.
Given the same xml file as before, the following code uses Sax to render the found person:

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
public class ElementMatchHandler extends DefaultHandler {
    public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException {
        SAXParser saxParser = SAXParserFactory.newInstance().newSAXParser();
        InputStream is = ElementMatchHandler.class.getResourceAsStream("sample.xml");
        ElementMatchHandler matchHandler = new ElementMatchHandler("person", "id", "001");
        saxParser.parse(is, matchHandler);
        Map found = matchHandler.getFound();
        if (found != null)
            System.out.println("matchHandler.getFound() = " + found);
        else
            System.out.println("Not found!");
    }
    private String elementName;
    private String matchElement;
    private String matchValue;
    private Map found;
    public ElementMatchHandler(String elementName, String matchElement, String matchValue) {
        this.elementName = elementName;
        this.matchElement = matchElement;
        this.matchValue = matchValue;
    }
    private boolean inElement;
    private Map elementMap = new HashMap();
    private StringBuffer tagText = new StringBuffer();
    private boolean isMatched;
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        if (qName.equals(elementName))
            inElement = true;
    }
    public void endElement(String uri, String localName, String qName) throws SAXException {
        super.endElement(uri, localName, qName);
        String text = tagText.toString().trim();
        if (qName.equals(elementName)) {
            if (isMatched)
                found = elementMap;
            isMatched = false;
            inElement = false;
        } else {
            if (inElement)
                elementMap.put(qName, text);
            if (qName.equals(matchElement) && text.equals(matchValue))
                isMatched = true;
        }
        tagText = new StringBuffer();
    }
    public void characters(char[] chars, int start, int length) throws SAXException {
        if (inElement)
            tagText.append(chars, start, length);
    }
    public Map getFound() {
        return found;
    }
}

Of course this code is incomplete and just fits the simple example, but that should give you an idea of what to do to get the job done.
Cheers

[Sebastian Green]

Thanks for your tips I will check them out right away (have been busy for a while). Im aware of the XPath, Im getting to soon but I need to understand the basic first. The next task will be XPath related. Thanks!