Parsing xml with DOM

The steps are

• Get a document builder using document builder factory and parse the xml file to create a DOM object
• Get a list of employee elements from the DOM
• For each employee element get the id,name,age and type. Create an employee value object and add it to the list.
• At the end iterate through the list and print the employees to verify we parsed it right.

Let us take this xml file:

<?xml version="1.0" encoding="UTF-8"?>
<Personnel>
  <Employee type="permanent">
        <Name>Seagull</Name>
        <Id>3674</Id>
        <Age>34</Age>
   </Employee>
  <Employee type="contract">
        <Name>Robin</Name>
        <Id>3675</Id>
        <Age>25</Age>
    </Employee>
  <Employee type="permanent">
        <Name>Crow</Name>
        <Id>3676</Id>
        <Age>28</Age>
    </Employee>
</Personnel>

Full code listing - DomParserExample

a) Getting a document builder

private void 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("employees.xml");


        }catch(ParserConfigurationException pce) {
            pce.printStackTrace();
        }catch(SAXException se) {
            se.printStackTrace();
        }catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }

b) Get a list of employee elements
Get the rootElement from the DOM object.From the root element get all employee elements. Iterate through each employee element to load the data.

 

private void parseDocument(){
        //get the root element
        Element docEle = dom.getDocumentElement();

        //get a nodelist of  elements
        NodeList nl = docEle.getElementsByTagName("Employee");
        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
                Employee e = getEmployee(el);

                //add it to list
                myEmpls.add(e);
            }
        }
    }

c) Reading in data from each employee.

/**
     * I take an employee element and read the values in, create
     * an Employee object and return it
     */
    private Employee getEmployee(Element empEl) {

        //for each <employee> element get text or int values of
        //name ,id, age and name
        String name = getTextValue(empEl,"Name");
        int id = getIntValue(empEl,"Id");
        int age = getIntValue(empEl,"Age");

        String type = empEl.getAttribute("type");

        //Create a new Employee with the value read from the xml nodes
        Employee e = new Employee(name,id,age,type);

        return e;
    }


    /**
     * 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 textVal;
    }


    /**
     * Calls getTextValue and returns a int value
     */
    private int getIntValue(Element ele, String tagName) {
        //in production application you would catch the exception
        return Integer.parseInt(getTextValue(ele,tagName));
    }

d) Iterating and printing.

private void printData(){

        System.out.println("No of Employees '" + myEmpls.size() + "'.");

        Iterator it = myEmpls.iterator();
        while(it.hasNext()) {
            System.out.println(it.next().toString());
        }
    }

See Xml parsing using sax.

Listing full code :

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

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.NodeList;
import org.xml.sax.SAXException;

public class DomParserExample {

    //No generics
    List myEmpls;
    Document dom;


    public DomParserExample(){
        //create a list to hold the employee objects
        myEmpls = new ArrayList();
    }

    public void runExample() {
        
        //parse the xml file and get the dom object
        parseXmlFile();
        
        //get each employee element and create a Employee object
        parseDocument();
        
        //Iterate through the list and print the data
        printData();
        
    }
    
    
    private void 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("employees.xml");
            

        }catch(ParserConfigurationException pce) {
            pce.printStackTrace();
        }catch(SAXException se) {
            se.printStackTrace();
        }catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }

    
    private void parseDocument(){
        //get the root elememt
        Element docEle = dom.getDocumentElement();
        
        //get a nodelist of <employee> elements
        NodeList nl = docEle.getElementsByTagName("Employee");
        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
                Employee e = getEmployee(el);
                
                //add it to list
                myEmpls.add(e);
            }
        }
    }


    /**
     * I take an employee element and read the values in, create
     * an Employee object and return it
     * @param empEl
     * @return
     */
    private Employee getEmployee(Element empEl) {
        
        //for each <employee> element get text or int values of 
        //name ,id, age and name
        String name = getTextValue(empEl,"Name");
        int id = getIntValue(empEl,"Id");
        int age = getIntValue(empEl,"Age");

        String type = empEl.getAttribute("type");
        
        //Create a new Employee with the value read from the xml nodes
        Employee e = new Employee(name,id,age,type);
        
        return e;
    }


    /**
     * 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  
     * @param ele
     * @param tagName
     * @return
     */
    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 textVal;
    }

    
    /**
     * Calls getTextValue and returns a int value
     * @param ele
     * @param tagName
     * @return
     */
    private int getIntValue(Element ele, String tagName) {
        //in production application you would catch the exception
        return Integer.parseInt(getTextValue(ele,tagName));
    }
    
    /**
     * Iterate through the list and print the 
     * content to console
     */
    private void printData(){
        
        System.out.println("No of Employees '" + myEmpls.size() + "'.");
        
        Iterator it = myEmpls.iterator();
        while(it.hasNext()) {
            System.out.println(it.next().toString());
        }
    }

    
    public static void main(String[] args){
        //create an instance
        DomParserExample dpe = new DomParserExample();
        
        //call run example
        dpe.runExample();
    }

}

Running DOMParserExample(JDK 1.5+)

1. Download DomParserExample.java, Employee.java, employees.xml to c:\xercesTest
   
2. Go to command prompt and type
   cd c:\xercesTest
   
3. To compile, type
   javac -classpath . DomParserExample.java
   
4. To run, type
   java -classpath . DomParserExample