Parsing xml using Java Dom Parser

Question

I am new to Java and XML and i need to fetch some data from an xml file.

Here is my xml

<?xml version="1.0" encoding="UTF-8"?>
<course name="BSc (Hons) Software Engineering" version="5.0" type="FT" lowerbound="2012" upperbound="2014" >
   <year id="1">
      <semester id="1">
         <module>
            <code>HCA1105C</code>
            <name>Computer Architecture</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>PROG1115C</code>
            <name>Object Oriented Software Development I</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MATH1103C</code>
            <name>Decision Mathematics</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
         <module>
            <code>ITE1107C</code>
            <name>Language and Communication Seminar</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
         <module>
            <code>MGMT1101C</code>
            <name>Management Seminar</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
      </semester>
      <semester id="2">
         <module>
            <code>PROG1116C</code>
            <name>Object Oriented Software Development II</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>WAT1116C</code>
            <name>Internet Programming I</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MATH1101C</code>
            <name>Analytic Methods for Computing</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>DBT1111C</code>
            <name>Database Design</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
      </semester>
   </year>
   <year id="2">
      <semester id="1">
         <module>
            <code>CAN2112C</code>
            <name>Network Design &amp; Programming</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>WAT2117C</code>
            <name>Internet Programming II</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>OSS2109C</code>
            <name>Operating Systems</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>PROG2117C</code>
            <name>Desktop Application Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
      </semester>
      <semester id="2">
         <module>
            <code>SDT2114C</code>
            <name>Requirements Engineering</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MATH2323C</code>
            <name>Numerical Methods</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MCT2104C</code>
            <name>Mobile Application Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MCT2104C</code>
            <name>Mobile Application Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>WAT2124C</code>
            <name>Web Services</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MGMT2104C</code>
            <name>Research &amp; Development Seminar</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
      </semester>
   </year>
   <year id="3">
      <semester id="1">
         <module>
            <code>SECU3119C</code>
            <name>Secure Software Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MULT3114C</code>
            <name>Game Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>SEM3112C</code>
            <name>Project Management Seminar</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
      </semester>
      <semester id="2">
         <module>
            <code>SDT3104C</code>
            <name>Enterprise Software Development</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>WAT3125C</code>
            <name>Emerging Web Technologies</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>SEM3113C</code>
            <name>Software Quality Management</name>
            <credits>4</credits>
            <hrs_per_wk>2+2</hrs_per_wk>
         </module>
         <module>
            <code>MGMT3105C</code>
            <name>Entrepreneurship Seminar</name>
            <credits>3</credits>
            <hrs_per_wk>2+1</hrs_per_wk>
         </module>
         <module>
            <code>PROJ3105C</code>
            <name>Systems Development Project</name>
            <credits>9</credits>
            <hrs_per_wk />
         </module>
      </semester>
   </year>
</course>

Lets say that i want to get all modules code that are in semester 1 year 1.

HCA1105C
PROG1115C
MATH1103C
ITE1107C
MGMT1101C

Here is my code so far

try {   
    File inputFile = new File(System.getProperty("user.dir") + "/courses/bse.xml");
        DocumentBuilderFactory dbFactory
                = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(inputFile);
        doc.getDocumentElement().normalize();
        NodeList nList = doc.getElementsByTagName("year");
        for (int i = 0; i < nList.getLength(); i++) {
            Node nNode = nList.item(i);
            if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                Element eElement = (Element) nNode;
               //if (Integer.parseInt(eElement.getAttribute("id")) == 1 ) {
                   System.out.println(eElement.getElementsByTagName("code").item(0).getTextContent());
               //}
            }
        }
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, e.getMessage(), "Fatal Error", JOptionPane.ERROR_MESSAGE);
        System.exit(1);
    }

I get the following output

HCA1105C
CAN2112C
SECU3119C

Yusuf K. · Accepted Answer · 2016-03-21 09:55:37Z

Checking child nodes and dive into for modules will give your expected result as below;

public static void main(String[] args) {
        try {
            File inputFile = new File("Snippet.xml");
            DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
            Document doc = dBuilder.parse(inputFile);
            doc.getDocumentElement().normalize();
            NodeList nList = doc.getElementsByTagName("year");
            for (int i = 0; i < nList.getLength(); i++) {
                Node nNode = nList.item(i);
                if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                    Element eElement = (Element) nNode;
                    if (Integer.parseInt(eElement.getAttribute("id")) == 1) { // Found year 1
                        NodeList semeterList = nNode.getChildNodes();
                        for (int j = 0; j < semeterList.getLength(); j++) {
                            nNode = semeterList.item(j);
                            if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                                Element semesterNode = (Element) nNode;
                                if (Integer.parseInt(semesterNode.getAttribute("id")) == 1) { //Found semester 1
                                    NodeList moduleList = semesterNode.getChildNodes();
                                    for (int k = 0; k < moduleList.getLength(); k++) {
                                        nNode = moduleList.item(k);
                                        if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                                            Element modeluNode = (Element) nNode;
                                            System.out.println(modeluNode.getElementsByTagName("code").item(0).getTextContent());
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            JOptionPane.showMessageDialog(null, e.getMessage(), "Fatal Error", JOptionPane.ERROR_MESSAGE);
            System.exit(1);
        }
    }

ajoshi · Accepted Answer · 2016-03-21 10:05:31Z

2

Your code is reading 1st module of every year. This is because, the node list will have 3 nodes (year=1, year=2, year=3) for the criteria you have specified.

If you want to read all modules of year 1, then you need to recurse in to the sub-section of the document with year="1". Then you will get nodelist of semesters. You need to further recurse in to children of semester=1.

You may try using query with xpath, where you can get the modules of year=1 and semester=1 directly.

http://viralpatel.net/blogs/java-xml-xpath-tutorial-parse-xml/

EDITED with modified code using XPath:

try {   
    File inputFile = new File("courses.xml");
        DocumentBuilderFactory dbFactory
                = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(inputFile);
        doc.getDocumentElement().normalize();

        XPath xPath =  XPathFactory.newInstance().newXPath();
        String expression = "/course/year[@id=1]/semester[@id=1]/module/code";
        NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(doc, XPathConstants.NODESET);
        System.out.println(expression);
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.println(nodeList.item(i).getTextContent()); 
        }
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, e.getMessage(), "Fatal Error", JOptionPane.ERROR_MESSAGE);
        System.exit(1);
    }

edited Mar 21, 2016 at 10:05

answered Mar 21, 2016 at 9:39

ajoshi

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1 Comment

trappski Over a year ago

A slight modification would be to fetch the module nodes and then get the code from there. Depending on if you need any of the extra information or not. But this should be the preferred answer though.

Naveen Singh · Accepted Answer · 2016-03-21 10:31:27Z

We can fetch all the codes through DOM, by using following code:

try {   
        File inputFile = new File("src/resources/res.xml");
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(inputFile);
        doc.getDocumentElement().normalize();
        NodeList nList = doc.getElementsByTagName("module");
        for (int i = 0; i < nList.getLength(); i++) {
             Node nNode = nList.item(i);
             if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                 Element eElement = (Element) nNode;
                 System.out.println(eElement.getElementsByTagName("code").item(0).getTextContent());
             }
        }
     } catch (Exception e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "Fatal Error", JOptionPane.ERROR_MESSAGE);
            System.exit(1);
      }

We can also, fetch code by looping each year --> semester --> module, then fetch the attribute code. Above code gives following results:

HCA1105C PROG1115C MATH1103C ITE1107C MGMT1101C PROG1116C WAT1116C MATH1101C DBT1111C CAN2112C WAT2117C OSS2109C PROG2117C SDT2114C MATH2323C MCT2104C MCT2104C WAT2124C MGMT2104C SECU3119C MULT3114C SEM3112C SDT3104C WAT3125C SEM3113C MGMT3105C PROJ3105C

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