Question

I am trying to parse the following XML file in Java and to store the XTimeStamp variable in an ArrayList and YVoltage in another ArrayList:

<?xml version = "1.0"?>
<Data>
<reading>
    <XTimeStamp> 12:00:00:01</XTimeStamp>
    <YVoltage>  0.6</YVoltage>
</reading>



<reading>
    <XTimeStamp> 12:00:00:02</XTimeStamp>
    <YVoltage>  0.5</YVoltage>
</reading>



<reading>
    <XTimeStamp> 12:00:00:025</XTimeStamp>
    <YVoltage>  0.5</YVoltage>
</reading>



<reading>
    <XTimeStamp> 12:00:00:031</XTimeStamp>
    <YVoltage>  0.1</YVoltage>
</reading>



<reading>
    <XTimeStamp> 12:00:00:039</XTimeStamp>
    <YVoltage>  -0.1</YVoltage>
</reading>



<reading>
    <XTimeStamp> 12:00:00:050</XTimeStamp>
    <YVoltage>  -0.2</YVoltage>
</reading>


<reading>
    <XTimeStamp> 12:00:01:01</XTimeStamp>
    <YVoltage>  0.01</YVoltage>
</reading>
</Data>

Here is the Java code I currently have to accomplish the task:

import java.util.*;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XMLReader {

    public static void main(String argv[]) {
        ArrayList XTimeStamp = new ArrayList();
        ArrayList YVoltage = new ArrayList();

        try {
            File file = new File("C:\\Users\\user\\My Documents\\MyXMLFile.xml");
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();
            Document doc = db.parse(file);
            doc.getDocumentElement().normalize();
            System.out.println("Root element "
                    + doc.getDocumentElement().getNodeName());
            NodeList nodeLst = doc.getElementsByTagName("reading");
            System.out.println("Data");

            for (int s = 0; s < nodeLst.getLength(); s++) {

                Node fstNode = nodeLst.item(s);

                if (fstNode.getNodeType() == Node.ELEMENT_NODE) {

                    Element fstElmnt = (Element) fstNode;
                    NodeList fstNmElmntLst = fstElmnt
                            .getElementsByTagName("XTimeStamp");
                    Element fstNmElmnt = (Element) fstNmElmntLst.item(0);
                    NodeList fstNm = fstNmElmnt.getChildNodes();
                    Element TimeStamp = (Element) fstNmElmntLst.item(0);
                    XTimeStamp.add(TimeStamp);
                    System.out.println("XTimeStamp : "
                            + ((Node) fstNm.item(0)).getNodeValue());
                    NodeList lstNmElmntLst = fstElmnt
                            .getElementsByTagName("YVoltage");
                    Element lstNmElmnt = (Element) lstNmElmntLst.item(0);
                    NodeList lstNm = lstNmElmnt.getChildNodes();
                    Element YValue = (Element) lstNm;
                    YVoltage.add(YValue);
                    System.out.println("YVoltage : "
                            + ((Node) lstNm.item(0)).getNodeValue());
                }

            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(XTimeStamp);
        System.out.println(YVoltage);
    }
}

When I run the code I am getting the following output, as can be seen from the listings of the ArrayLists at the bottom there is a problem:

Root element Data
Data
XTimeStamp :  12:00:00:01
YVoltage :   0.6
XTimeStamp :  12:00:00:02
YVoltage :   0.5
XTimeStamp :  12:00:00:025
YVoltage :   0.5
XTimeStamp :  12:00:00:031
YVoltage :   0.1
XTimeStamp :  12:00:00:039
YVoltage :   -0.1
XTimeStamp :  12:00:00:050
YVoltage :   -0.2
XTimeStamp :  12:00:01:01
YVoltage :   0.01
[[XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null],  [XTimeStamp: null], [XTimeStamp: null]]
[[YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null]]

Any help with this would be much appreciated.

Thanks.

Answer 1

Try this:

Instead of:

Element TimeStamp = (Element) fstNmElmntLst.item(0);
XTimeStamp.add(TimeStamp);

Do (if you can add Strings to XTimeStamp):

String timeStamp = fstNm.item(0)).getNodeValue(); 
XTimeStamp.add(timeStamp);

Or do this if you want to save Elements (I’d recommend you to save the Strings)

Element timeStamp = (Element) fstNm.item(0)); 
XTimeStamp.add(timeStamp);

Remember that the convention in Java is to name the variables with the first letter lowercase.