Parsing an XML document using DOM

Aim:

            To create simple DOM parser to parse XML document

Algorithm:

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

Program:

DomParserExample.java

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();

            }

}

Employee.java

public class Employee {

            private String name;

            private int age;

           

            private int id;

            private String type;

           

            public Employee(){

                       

            }

           

            public Employee(String name, int id, int age,String type) {

                        this.name = name;

                        this.age = age;

                        this.id  = id;

                        this.type = type;

                       

            }

            public int getAge() {

                        return age;

            }

            public void setAge(int age) {

                        this.age = age;

            }

            public int getId() {

                        return id;

            }

            public void setId(int id) {

                        this.id = id;

            }

            public String getName() {

                        return name;

            }

            public void setName(String name) {

                        this.name = name;

            }

            public String getType() {

                        return type;

            }

            public void setType(String type) {

                        this.type = type;

            }          

           

           

            public String toString() {

                        StringBuffer sb = new StringBuffer();

                        sb.append("Employee Details - ");

                        sb.append("Name:" + getName());

                        sb.append(", ");

                        sb.append("Type:" + getType());

                        sb.append(", ");

                        sb.append("Id:" + getId());

                        sb.append(", ");

                        sb.append("Age:" + getAge());

                        sb.append(".");

                       

                        return sb.toString();

            }

}

 Employees.xml

<?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>