In this tutorial we are going to see how to use the built in Java DOM parser in order to parse an XML file into a DOM Object As you might know, the DOM object has the classic Tree Structure with nodes, elements, attributes etc… Remember that DOM parser reads the XML file and constructs the DOM object in the memory. Then, you have to traverse the DOM like you would do a tree structure, node by node to get the element you want. Of course there are some more advanced parsers (like Jsoup for instance, witch is more for HTML Parsing) that offer more flexible APIs.
As we said, the DOM parser creates the DOM object in its whole inside the memory. So as you can imagine this might be memory consuming for large files. You can always use a SAX parser to get around this problem.
Here we have a simple XML File:
testFile.xml
<?xml version="1.0"?>
<company>
<employee id="1">
<firstname>James</firstname>
<lastname>Harley</lastname>
<email>james@example.org</email>
<department>Human Resources</department>
<salary>1000</salary>
</employee>
<employee id="2">
<firstname>John</firstname>
<lastname>May</lastname>
<email>john@example.org</email>
<department>Logistics</department>
<salary>400</salary>
</employee>
</company>ReadXMLFileUsingDom.java
package com.javacodegeeks.java.core;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;
import java.io.File;
public class ReadXMLFileUsingDom {
public static final String xmlFilePath = "C:\\Users\\nikos7\\Desktop\\files\\testFile.xml";
public static void main(String argv[]) {
try {
File xmlFile = new File(xmlFilePath);
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document doc = documentBuilder.parse(xmlFile);
doc.getDocumentElement().normalize();
System.out.println("Root element :" + doc.getDocumentElement().getNodeName());
NodeList nodeList = doc.getElementsByTagName("employee");
System.out.println("===============================================================");
//do this the old way, because nodeList is not iterable
for (int itr = 0; itr < nodeList.getLength(); itr++) {
Node node = nodeList.item(itr);
System.out.println("\nNode Name :" + node.getNodeName());
if (node.getNodeType() == Node.ELEMENT_NODE) {
Element eElement = (Element) node;
System.out.println("Employee id : "
+ eElement.getAttribute("id"));
System.out.println("First Name : "
+ eElement.getElementsByTagName("firstname")
.item(0).getTextContent());
System.out.println("Last Name : "
+ eElement.getElementsByTagName("lastname").item(0)
.getTextContent());
System.out.println("Email : "
+ eElement.getElementsByTagName("email").item(0)
.getTextContent());
System.out.println("Department : "
+ eElement.getElementsByTagName("department").item(0)
.getTextContent());
System.out.println("Salary : "
+ eElement.getElementsByTagName("salary").item(0)
.getTextContent());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}Output:
Root element :company
===============================================================
Node Name :employee
Employee id : 1
First Name : James
Last Name : Harley
Email : james@example.org
Department : Human Resources
Salary : 1000
Node Name :employee
Employee id : 2
First Name : John
Last Name : May
Email : john@example.org
Department : Logistics
Salary : 400
Now let’s see how to read and parse the XML file to a DOM object and loop the nodes one by one printing element and attribute names and values.
package com.javacodegeeks.java.core;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class ReadXMLFileUsingDom {
public static final String xmlFilePath = "C:\\Users\\nikos7\\Desktop\\files\\testFile.xml";
public static void main(String[] args) {
try {
File xmlFile = new File(xmlFilePath);
DocumentBuilder documentBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document document = documentBuilder.parse(xmlFile);
System.out.println("Root element :"+ document.getDocumentElement().getNodeName());
System.out.println("===============================");
if (document.hasChildNodes()) {
printNodeList(document.getChildNodes());
}
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
private static void printNodeList(NodeList nodeList) {
for (int count = 0; count < nodeList.getLength(); count++) {
Node elemNode = nodeList.item(count);
if (elemNode.getNodeType() == Node.ELEMENT_NODE) {
// get node name and value
System.out.println("\nNode Name =" + elemNode.getNodeName()
+ " [OPEN]");
System.out.println("Node Content =" + elemNode.getTextContent());
if (elemNode.hasAttributes()) {
NamedNodeMap nodeMap = elemNode.getAttributes();
for (int i = 0; i < nodeMap.getLength(); i++) {
Node node = nodeMap.item(i);
System.out.println("attr name : " + node.getNodeName());
System.out.println("attr value : "
+ node.getNodeValue());
}
}
if (elemNode.hasChildNodes()) {
//recursive call if the node has child nodes
printNodeList(elemNode.getChildNodes());
}
System.out.println("Node Name =" + elemNode.getNodeName()
+ " [CLOSE]");
}
}
}
}
Output:
Root element :company
===============================
Node Name =company
Node Content =
James
Harley
james@example.org
Human Resources
1000
John
May
john@example.org
Logistics
400
Node Name =employee
Node Content =
James
Harley
james@example.org
Human Resources
1000
attr name : id
attr value : 1
Node Name =firstname
Node Content =James
Node Name =lastname
Node Content =Harley
Node Name =email
Node Content =james@example.org
Node Name =department
Node Content =Human Resources
Node Name =salary
Node Content =1000
Node Name =employee
Node Content =
John
May
john@example.org
Logistics
400
attr name : id
attr value : 2
Node Name =firstname
Node Content =John
Node Name =lastname
Node Content =May
Node Name =email
Node Content =john@example.org
Node Name =department
Node Content =Logistics
Node Name =salary
Node Content =400
This was an example on how to read XML File in Java using DOM parser.
