Dom Parser picking up only first tag

[Lou Pelagalli]

Hi,

My Dom parser is picking up only the first tag, in this case <gram>. Can someone tell me why <carat> is not included?

Code and console output below.

Thanks,

Lou

XML file MKSFactors2.xml
<?xml version="1.0" encoding="UTF-8"?> <conversions> <weights><!--MKS = Grams--> <label>Weight</label> <gram> <type>Metric</type> <name>Gram</name> <toMKS>1</toMKS> <fromMKS>1</fromMKS> </gram> <carat> <type>Metric</type> <name>Carat (ct)</name> <toMKS>5</toMKS> <fromMKS>0.2</fromMKS> </carat> </weights> </conversions>


DomParser.java

import java.io.IOException;
import java.util.Iterator;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.util.ArrayList;

import org.xml.sax.SAXException;
public class DomParser {
	Document dom;
	ArrayList<Measurement> measurements = new ArrayList<Measurement>();
	
	public void parseXmlFile(){
		System.out.println("DomParser.parseXmlFile()");
		//get the factory
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

		try {

			//Using factory get an instance of document builder
			DocumentBuilder db = dbf.newDocumentBuilder();

			//parse using builder to get DOM representation of the XML file
			dom = db.parse("MKSFactors2.xml");
			System.out.println("dom=" + dom);

		}catch(ParserConfigurationException pce) {
			pce.printStackTrace();
		}catch(SAXException se) {
			se.printStackTrace();
		}catch(IOException ioe) {
			ioe.printStackTrace();
		}
	}
	public void parseDocument(){
		System.out.println("parseDocument()");
		//get the root element
		Element docEle = dom.getDocumentElement();

		//get a nodelist of  elements
		NodeList nl = docEle.getElementsByTagName("weights");
		if(nl != null && nl.getLength() > 0) {
			for(int i = 0 ; i < nl.getLength();i++) {

				//get the employee element
				Element el = (Element)nl.item(i);

				//get the Employee object
				Measurement m = getMeasurement(el);

				//add it to list
				measurements.add(m);
				System.out.println("Measurement Added");
			}
		}

	}
	

	/**
	 * I take an employee element and read the values in, create
	 * an Employee object and return it
	 */
	private Measurement getMeasurement(Element element) {
		System.out.println("getMeasurement(Element element)");
		//for each <Measurement> element get text or int values of
		//label, type, toMKS and fromMKS
		String label = getTextValue(element,"label");
		String type = getTextValue(element,"type");
		String name = getTextValue(element,"name");
		float toMKS = getFloatValue(element,"toMKS");
		float fromMKS = getFloatValue(element,"fromMKS");
		
		//Create a new Measurement with the value read from the xml nodes
		Measurement measurement = new Measurement(label, type, name, toMKS, fromMKS);
		
		return measurement;
	}


	/**
	 * I take a xml element and the tag name, look for the tag and get
	 * the text content
	 * i.e for <employee><name>John</name></employee> xml snippet if
	 * the Element points to employee node and tagName is 'name' I will return John
	 */
	private String getTextValue(Element ele, String tagName) {
		String textVal = null;
		NodeList nl = ele.getElementsByTagName(tagName);
		if(nl != null && nl.getLength() > 0) {
			Element el = (Element)nl.item(0);
			textVal = el.getFirstChild().getNodeValue();
		}

		return (null == textVal) ? "" : textVal;
	}


	/**
	 * Calls getTextValue and returns a float value
	 */
	private float getFloatValue(Element element, String tagName) {
		//in production application you would catch the exception
		return Float.parseFloat(getTextValue(element,tagName));
	}

	public void printData(){

		System.out.println("Number of Measurements = " + measurements.size() + ".");

		Iterator<Measurement> it = measurements.iterator();
		while(it.hasNext()) {
			Measurement measurement = (Measurement)it.next();
			System.out.println("Measurement label=" + measurement.getLabel() + ", type=" + measurement.getType()
                                + ", name=" + measurement.getName() + ", toMKS=" + measurement.getToMKS()
                                + ", fromMKS=" + measurement.getFromMKS());
			//System.out.println(it.next().toString());
		}
	}
}

Console Output
Starting MeasurementList
DomParser.parseXmlFile()
dom=[#document: null]
parseDocument()
getMeasurement(Element element)
Measurement Added
Number of Measurements = 1.
Measurement label=Weight, type=Metric, name=Gram, toMKS=1.0, fromMKS=1.0

[Ulf Dittmer]

I was going to try running it, but the Measurement class is missing. Please post an SSCCE (<-- that's a link), or post the missing class(es).

[William Brogden]

textVal = el.getFirstChild().getNodeValue();

I always suspect that getFirstChild() returns some formatting crlf or spaces, and not the Node you are expecting.

Bill

[Lou Pelagalli]

Hi Ulf,

Sorry I didn't post all the classes.

All files follow my signature.

MeasurementList is the main class.

MKSFactors2.xml is a small file for testing and development. I have a much larger file for production after I get the smaller one working.

Thanks,

Lou

MeasurementList.java

public class MeasurementList {
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		System.out.println("Starting MeasurementList");
		DomParser dp = new DomParser();
		dp.parseXmlFile();
		dp.parseDocument();
		dp.printData();
	}
}

Measurement.java

public class Measurement {
	private String label;
	private String type;
	private String name;
	private float toMKS;
	private float fromMKS;
	
	private Measurement() {
	}
	
	public Measurement(String label, String type, String name, float toMKS, float fromMKS){
		this.label = label;
		this.type = type;
		this.name = name;
		this.toMKS = toMKS;
		this.fromMKS = fromMKS;
		
	}
	
	public String getLabel() {
		return this.label;
	}

	public String getType() {
		return this.type;
	}
	
	public String getName() {
		return this.name;
	}

	public float getToMKS() {
		return this.toMKS;
	}

	public float getFromMKS() {
		return this.fromMKS;
	}
}

DomParser.java

import java.io.IOException;
import java.util.Iterator;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.util.ArrayList;

import org.xml.sax.SAXException;
public class DomParser {
	Document dom;
	ArrayList<Measurement> measurements = new ArrayList<Measurement>();
	
	public void parseXmlFile(){
		System.out.println("DomParser.parseXmlFile()");
		//get the factory
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

		try {

			//Using factory get an instance of document builder
			DocumentBuilder db = dbf.newDocumentBuilder();

			//parse using builder to get DOM representation of the XML file
			dom = db.parse("MKSFactors2.xml");
			System.out.println("dom=" + dom);

		}catch(ParserConfigurationException pce) {
			pce.printStackTrace();
		}catch(SAXException se) {
			se.printStackTrace();
		}catch(IOException ioe) {
			ioe.printStackTrace();
		}
	}
	public void parseDocument(){
		System.out.println("parseDocument()");
		//get the root element
		Element docEle = dom.getDocumentElement();

		//get a nodelist of  elements
		NodeList nl = docEle.getElementsByTagName("weights");
		if(nl != null && nl.getLength() > 0) {
			for(int i = 0 ; i < nl.getLength();i++) {

				//get the measurement element
				Element el = (Element)nl.item(i);

				//get the Measurement object
				Measurement m = getMeasurement(el);

				//add it to list
				measurements.add(m);
				System.out.println("Measurement Added");
			}
		}
	}

	/**
	 * I take an measurement element and read the values in, create
	 * a measurement object and return it
	 */
	private Measurement getMeasurement(Element element) {
		System.out.println("getMeasurement(Element element)");
		//for each <Measurement> element get text or int values of
		//label, type, toMKS and fromMKS
		String label = getTextValue(element,"label");
		String type = getTextValue(element,"type");
		String name = getTextValue(element,"name");
		float toMKS = getFloatValue(element,"toMKS");
		float fromMKS = getFloatValue(element,"fromMKS");
		
		//Create a new Measurement with the value read from the xml nodes
		Measurement measurement = new Measurement(label, type, name, toMKS, fromMKS);
		
		return measurement;
	}


	/**
	 * I take a xml element and the tag name, look for the tag and get
	 * the text content
	 * i.e for <weights><gram><type>Metric</type></gram></weights> xml snippet if
	 * the Element points to measurement node and tagName is 'name' I will return John
	 */
	private String getTextValue(Element ele, String tagName) {
		String textVal = null;
		NodeList nl = ele.getElementsByTagName(tagName);
		if(nl != null && nl.getLength() > 0) {
			Element el = (Element)nl.item(0);
			textVal = el.getFirstChild().getNodeValue();
		}

		return (null == textVal) ? "" : textVal;
	}


	/**
	 * Calls getTextValue and returns a float value
	 */
	private float getFloatValue(Element element, String tagName) {
		//in production application you would catch the exception
		return Float.parseFloat(getTextValue(element,tagName));
	}

	public void printData(){

		System.out.println("Number of Measurements = " + measurements.size() + ".");

		Iterator<Measurement> it = measurements.iterator();
		while(it.hasNext()) {
			Measurement measurement = (Measurement)it.next();
			System.out.println("Measurement label=" + measurement.getLabel() + ", type=" + measurement.getType()
                                  + ", name=" + measurement.getName() + ", toMKS=" + measurement.getToMKS() 
                                  + ", fromMKS=" + measurement.getFromMKS());
			//System.out.println(it.next().toString());
		}
	}
}

MKSFactors2.xml
<?xml version="1.0" encoding="UTF-8"?> <conversions> <weights><!--MKS = Grams--> <label>Weight</label> <gram> <type>Metric</type> <name>Gram</name> <toMKS>1</toMKS> <fromMKS>1</fromMKS> </gram> <carat> <type>Metric</type> <name>Carat (ct)</name> <toMKS>5</toMKS> <fromMKS>0.2</fromMKS> </carat> </weights> </conversions>

[Ulf Dittmer]

After a quick look at the code, I don't see how it could be adding more measurements to the list than a single one. In the parseDocument method it adds one measurement for each "weights" tag - of which there is only one. I think you need to iterate through all the children of the weights node, and add them as appropriate.