Get line number from xml node - java

Question

I have parsed an XML file and have gotten a Node that I am interested in. How can I now find the line number in the source XML file where this node occurs?

EDIT: Cur

Answer 1

If you are using a SAX parser then the line number of an event can be obtained using the Locator object, which is notified to the ContentHandler via the setDocumentLocator() callback. This is called at the start of parsing, and you need to save the Locator; then after any event (such as startElement()), you can call methods such as getLineNumber() to obtain the current position in the source file. (After startElement(), the callback is defined to give you the line number on which the ">" of the start tag appears.)

Answer 2

priomsrb's answer is great and works. For my usecase i need to integrate it to an existing framework where e.g. the encoding is also covered. Therefore the following refactoring was applied to have a separate LineNumberHandler class.

Then the code will also work with a Sax InputSource where the encoding can be modified like this:

            // read in the xml document
            org.xml.sax.InputSource is=new org.xml.sax.InputSource();
            is.setByteStream(instream);
            if (encoding!=null) {
                is.setEncoding(encoding);
                if (Debug.CORE)
                    Debug.log("setting XML encoding to - "+is.getEncoding());
            }   

Separate LineNumberHandler

/**
 * LineNumber Handler
 * @author wf
 *
 */
public static class LineNumberHandler extends DefaultHandler {

final Stack<Element> elementStack = new Stack<Element>();
final StringBuilder textBuffer = new StringBuilder();
private Locator locator;
private Document doc;

/**
 * create a line number Handler for the given document
 * @param doc
 */
public LineNumberHandler(Document doc) {
  this.doc=doc;
}

@Override
public void setDocumentLocator(final Locator locator) {
  this.locator = locator; // Save the locator, so that it can be used
                          // later for line tracking when traversing
                          // nodes.
}

@Override
public void startElement(final String uri, final String localName,
    final String qName, final Attributes attributes) throws SAXException {
  addTextIfNeeded();
  final Element el = doc.createElement(qName);
  for (int i = 0; i < attributes.getLength(); i++) {
    el.setAttribute(attributes.getQName(i), attributes.getValue(i));
  }
  el.setUserData(LINE_NUMBER_KEY_NAME,
      String.valueOf(this.locator.getLineNumber()), null);
  elementStack.push(el);
}

@Override
public void endElement(final String uri, final String localName,
    final String qName) {
  addTextIfNeeded();
  final Element closedEl = elementStack.pop();
  if (elementStack.isEmpty()) { // Is this the root element?
    doc.appendChild(closedEl);
  } else {
    final Element parentEl = elementStack.peek();
    parentEl.appendChild(closedEl);
  }
}

@Override
public void characters(final char ch[], final int start, final int length)
    throws SAXException {
  textBuffer.append(ch, start, length);
}

// Outputs text accumulated under the current node
private void addTextIfNeeded() {
  if (textBuffer.length() > 0) {
    final Element el = elementStack.peek();
    final Node textNode = doc.createTextNode(textBuffer.toString());
    el.appendChild(textNode);
    textBuffer.delete(0, textBuffer.length());
  }
}

};

PositionalXMLReader

public class PositionalXMLReader {
  final static String LINE_NUMBER_KEY_NAME = "lineNumber";
 /**
  * read a document from the given input strem
  * 
  * @param is
  *          - the input stream
  * @return - the Document
  * @throws IOException
  * @throws SAXException
  */
public static Document readXML(final InputStream is)
  throws IOException, SAXException {
  final Document doc;
  SAXParser parser;
    try {
      final SAXParserFactory factory = SAXParserFactory.newInstance();
      parser = factory.newSAXParser();
      final DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory
      .newInstance();
      final DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
      doc = docBuilder.newDocument();
    } catch (final ParserConfigurationException e) {
      throw new RuntimeException("Can't create SAX parser / DOM builder.", e);
    }
    LineNumberHandler handler = new LineNumberHandler(doc);
    parser.parse(is, handler);

    return doc;
  }
}

JUnit Testcase

package com.bitplan.common.impl;

import static org.junit.Assert.assertEquals;

import java.io.ByteArrayInputStream;
import java.io.InputStream;

import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Node;

import com.bitplan.bobase.PositionalXMLReader;

public class TestXMLWithLineNumbers {

  /**
   * get an Example XML Stream
   * @return the example stream
   */
  public InputStream getExampleXMLStream() {
    String xmlString = "<foo>\n" + "    <bar>\n"
        + "        <moo>Hello World!</moo>\n" + "    </bar>\n" + "</foo>";

    InputStream is = new ByteArrayInputStream(xmlString.getBytes());
    return is;
  }

  @Test
  public void testXMLWithLineNumbers() throws Exception {
    InputStream is = this.getExampleXMLStream();
    Document doc = PositionalXMLReader.readXML(is);
    is.close();

    Node node = doc.getElementsByTagName("moo").item(0);
    assertEquals("3", node.getUserData("lineNumber"));
  }  
}

Answer 3

I have got this working by following this example:

http://eyalsch.wordpress.com/2010/11/30/xml-dom-2/

This solution follows the method suggested by Michael Kay. Here is how you use it:

// XmlTest.java

import java.io.ByteArrayInputStream;
import java.io.InputStream;

import org.w3c.dom.Document;
import org.w3c.dom.Node;

public class XmlTest {
    public static void main(final String[] args) throws Exception {

        String xmlString = "<foo>\n"
                         + "    <bar>\n"
                         + "        <moo>Hello World!</moo>\n"
                         + "    </bar>\n"
                         + "</foo>";

        InputStream is = new ByteArrayInputStream(xmlString.getBytes());
        Document doc = PositionalXMLReader.readXML(is);
        is.close();

        Node node = doc.getElementsByTagName("moo").item(0);

        System.out.println("Line number: " + node.getUserData("lineNumber"));
    }
}

If you run this program, it will out put: "Line number: 3"

PositionalXMLReader is a slightly modified version of the example linked above.

// PositionalXMLReader.java

import java.io.IOException;
import java.io.InputStream;
import java.util.Stack;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.Attributes;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class PositionalXMLReader {
    final static String LINE_NUMBER_KEY_NAME = "lineNumber";

    public static Document readXML(final InputStream is) throws IOException, SAXException {
        final Document doc;
        SAXParser parser;
        try {
            final SAXParserFactory factory = SAXParserFactory.newInstance();
            parser = factory.newSAXParser();
            final DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
            final DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
            doc = docBuilder.newDocument();
        } catch (final ParserConfigurationException e) {
            throw new RuntimeException("Can't create SAX parser / DOM builder.", e);
        }

        final Stack<Element> elementStack = new Stack<Element>();
        final StringBuilder textBuffer = new StringBuilder();
        final DefaultHandler handler = new DefaultHandler() {
            private Locator locator;

            @Override
            public void setDocumentLocator(final Locator locator) {
                this.locator = locator; // Save the locator, so that it can be used later for line tracking when traversing nodes.
            }

            @Override
            public void startElement(final String uri, final String localName, final String qName, final Attributes attributes)
                    throws SAXException {
                addTextIfNeeded();
                final Element el = doc.createElement(qName);
                for (int i = 0; i < attributes.getLength(); i++) {
                    el.setAttribute(attributes.getQName(i), attributes.getValue(i));
                }
                el.setUserData(LINE_NUMBER_KEY_NAME, String.valueOf(this.locator.getLineNumber()), null);
                elementStack.push(el);
            }

            @Override
            public void endElement(final String uri, final String localName, final String qName) {
                addTextIfNeeded();
                final Element closedEl = elementStack.pop();
                if (elementStack.isEmpty()) { // Is this the root element?
                    doc.appendChild(closedEl);
                } else {
                    final Element parentEl = elementStack.peek();
                    parentEl.appendChild(closedEl);
                }
            }

            @Override
            public void characters(final char ch[], final int start, final int length) throws SAXException {
                textBuffer.append(ch, start, length);
            }

            // Outputs text accumulated under the current node
            private void addTextIfNeeded() {
                if (textBuffer.length() > 0) {
                    final Element el = elementStack.peek();
                    final Node textNode = doc.createTextNode(textBuffer.toString());
                    el.appendChild(textNode);
                    textBuffer.delete(0, textBuffer.length());
                }
            }
        };
        parser.parse(is, handler);

        return doc;
    }
}

Answer 4

Note that according to the spec (of Locator.getLineNumber()) the method returns the line number where the SAX-event ends!

In the case of "startElement()" this means:

Here the line number for Element is 1:

<Element></Element>

Here the line number for Element is 3:

<Element
   attribute1="X"
   attribute2="Y">
</Element>