JAVA XML - How do I get specific elements in an XML Node?

Question

This is an academic assignment and we are given an extremely large XML file with hundreds of entries like these. For each item we are supposed to list the Manager's ID, the Person's ID of the last person to add an item to the list, and the current number of items. I have read and reread the Oracle DOM API and various Node APIs. We are using JAVA and I cannot for the life of me figure out how to search various 'fields' of each item_list node. Below is an example of the data we are given.

<item_list id="item_list01">
   <numitems_intial>5</numitems_initial>
   <item>
     <date_added>1/1/2014</date_added>
     <added_by person="person01" />
   </item>
   <item>
      <date_added>1/6/2014</date_added>
      <added_by person="person05" />
    </item>
    <numitems_current>7</numitems_current>
    <manager person="person48" />
</item_list>
<item_list id="item_list02">
   <numitems_intial>5</numitems_initial>
   <item>
     <date_added>1/15/2014</date_added>
     <added_by person="person05" />
   </item>
   <item>
     <date_added>1/1/2014</date_added>
     <added_by person="person09" />
   </item>
       <item>
         <date_added>1/9/2014</date_added>
         <added_by person="person45" />
       </item>
        <numitems_current>7</numitems_current>
        <manager person="person38" />
    </item_list>

I've tried doing something similar to:

NodeList nodes = queryDoc.getElementsByTagName("item_list");

for(int i = 0; i < nodes.getLength(); i++) {

    Node node = nodes.item(i);

    if(node != null) {

       System.out.println(node.manager);

    }

}

And messing around with this code for a while, but I would like to know how to retrieve data from various fields in each node.

Answer 1

If you are trying to read person attribute of manager tag, you can do it as shown below -

import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;


public class Test{

public static void main (String[] args)
{
    Test test = new Test();
    test.readXML();
}

private void readXML()
{
    Document doc = null;
    try 
    {
        doc = parseXML("/home/abc/Test.xml");
    } 
    catch (ParserConfigurationException e) 
    {
        e.printStackTrace();
    } 
    catch (SAXException e) 
    {
        e.printStackTrace();
    } 
    catch (IOException e) 
    {
        e.printStackTrace();
    }

    if(doc != null)
    {
        NodeList nList = doc.getElementsByTagName("item_list");
        for (int i = 0; i < nList.getLength(); i++) 
        {
            Node nNode = nList.item(i);
            Element eElement = (Element) nNode;
            Element cElement =  (Element) eElement.getElementsByTagName("manager").item(0);
            System.out.println("Manager ID : " + cElement.getAttribute("person"));
        }
    }
}

private Document parseXML(String filePath) throws ParserConfigurationException, SAXException, IOException
{
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    Document doc = db.parse(filePath);
    doc.getDocumentElement().normalize();
    return doc;
}
}

Answer 2

Or, using xml you might need to edit the initial content. I suggest the following approach

import java.io.IOException;
import java.io.StringWriter;

import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.*;
import org.xml.sax.SAXException;


public class ReadXML {

    public static void main(String[] args) {
        try {
            Document doc = getDocument("/home/abc/Test.xml");

            System.out.println(getString(getNodeByName(doc,"item_list01")));
        } catch (TransformerException | ParserConfigurationException | IOException | SAXException e) {
            // Log e.printStackTrace();
        }
    }

    private static Document getDocument(String filePath) throws ParserConfigurationException, IOException, SAXException {
        DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = dbfac.newDocumentBuilder();

        return docBuilder.parse(filePath);
    }

    private static String getString(Node node) throws TransformerException {
        StringWriter sw = new StringWriter();
        Transformer t = TransformerFactory.newInstance().newTransformer();
        t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        t.setOutputProperty(OutputKeys.INDENT, "yes");
        t.transform(new DOMSource(node), new StreamResult(sw));

        return sw.toString();
    }

    public static Node getNodeByName(Document doc, String nodeName) {
        Node node = null;
        for (int i = 0; i < doc.getDocumentElement().getChildNodes().getLength(); i++) {
            if (!getTagName(doc, i).equals("#text")) {
                for (int j = 0; j < getNodeName(doc, i).getChildNodes().getLength(); j++) {
                    if (getNodeName(doc, i, j).equalsIgnoreCase("item_list")  && getNodeAttributes(doc,i,j).equalsIgnoreCase(nodeName)) {
                        node = getNodeName(doc, i);
                    }
                }
            }
        }
        return node;
    }

    private static String getTagName(Document doc, int i) {
        return getNodeName(doc, i).getNodeName();
    }

    private static Node getNodeName(Document doc, int i) {
        return (doc.getDocumentElement().getChildNodes().item(i));
    }

    private static String getNodeName(Document doc, int i, int j) {
        return getNodeName(doc, i).getChildNodes().item(j).getNodeName();
    }
    private static String getNodeAttributes(Document doc, int i, int j) {
        if(getNodeName(doc, i).getChildNodes().item(j).hasAttributes()){
            return getNodeName(doc, i).getChildNodes().item(j).getAttributes().item(0).getNodeValue();
        }
        return "";
    }
}