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

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 elementStack = new Stack();
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 = "\n" + "    \n"
        + "        Hello World!\n" + "    \n" + "";

    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"));
  }  
}