XML DOM Parser in Java

XML DOM Parser in Java

In this section  we are discussing about  XML DOM Parser in Java.  DOM is the abbreviation of Document Object Model. XML DOM  in Java is available with JDK itself .This parser is not suitable if we need to manipulate XML file of large size. Because if we read an XML file using DOM parser , then it loads into memory after parsing.Then traversal through is easy . But for large sized files , loading the entire content to memory is not feasible always.

Reading XML File using DOM Parser

 Now let us see how to read an XML file using DOM Parser. The steps  for reading an XML are:

1)Create  DocumentBuilderFactory and DocumentBuilder objects

2)Create a document using the DocumentBuilder object created earlier by passing the input XML file as argument.

3)Find the nodes of the document

4)Find each element in a node

5)Iterate through all nodes till the end

Now let us see the student.xml. It is giving as the input to Java program.




Bijoy
10 A

The XML document  contains details of students in a school.As of now I just included details of only one student.We can give any number of student elements under the school tag.Now see the Java code to parse the student.xml

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;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.File;
import java.io.IOException;
public class XMLReadDOM {
public XMLReadDOM() {

}
public void readXML() {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse(new File("C:\\Users\\My PC\\Projects\\Sample\\files\\student.xml"));
NodeList list = document.getElementsByTagName("student");
for (int i = 0; i < list.getLength(); i++) { Node node = list.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) { Element element = (Element) node; System.out.println("Id = " + element.getAttribute("id")); System.out.println("Name = " + element.getElementsByTagName("name").item(0).getTextContent()); System.out.println("Class / Batch = " + element.getElementsByTagName("class").item(0).getTextContent()); System.out.println("Division = " + element.getElementsByTagName("division").item(0).getTextContent()); } } } catch (ParserConfigurationException e) { e.printStackTrace(); } catch (SAXException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) { XMLReadDOM xmlReadDOM = new XMLReadDOM(); xmlReadDOM.readXML(); } }

Now let us see the output.

Output

Id = 1

Name = Bijoy

Class / Batch = 10

Division = A

You can add more students to the XML file and verify the result.

For example if I added one more student in XML , then the student.xml:




Bijoy
10 A


Karthik
10 B

Now the output will become:

Id = 1

Name = Bijoy

Class / Batch = 10

Division = A

Id = 2

Name = Karthik

Class / Batch = 10

Division = B

Now let us see how to write data to an XML file using XML DOM Parser in Java.

Writing to XML file using DOM

The steps in writing data to an XML file are :

1)Create DocumentBuilderFactory and DocumentBuilder objects.

2)Create Document object.

3)Construct the document from top to bottom.

4)Create  TransFormerFactory and Transform objects to transform the created Document  object to file

5)Transform the document to xml file.

The  Java code is shown below. It creates s student1.xml  in a path mentioned in the code.

import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.File;
public class XMLWriteDOM {
public XMLWriteDOM() {

}

public void writeXML() {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.newDocument();
Element baseElement = document.createElement("school");
document.appendChild(baseElement);
Element student = document.createElement("student");
baseElement.appendChild(student);
Attr attr = document.createAttribute("id");
attr.setValue("1");
student.setAttributeNode(attr);
Element name = document.createElement("name");
name.appendChild(document.createTextNode("Bijoy"));
student.appendChild(name);
Element batch = document.createElement("class");
batch.appendChild(document.createTextNode("10"));
student.appendChild(batch);
Element division = document.createElement("division");
division.appendChild(document.createTextNode("A"));
student.appendChild(division);
TransformerFactory tfrFactory = TransformerFactory.newInstance();
Transformer transformer = tfrFactory.newTransformer();
DOMSource domSource = new DOMSource(document);
StreamResult streamResult = new StreamResult(new File("C:\\Users\\My PC\\Projects\\Sample\\files\\student1.xml"));
transformer.transform(domSource, streamResult);
System.out.println("Done");
} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (TransformerConfigurationException e) {
e.printStackTrace();
} catch (TransformerException e) {
e.printStackTrace();
}
}

public static void main(String[] args) {
XMLWriteDOM xmlWriteDOM = new XMLWriteDOM();
xmlWriteDOM.writeXML();
}
}

Now let us check for the student1.xml file in the mentioned path of StreamResult object.

student1.xml




Bijoy
10 A

See also:

XML Processing in Java

SAX Interface

StAX interface

JAXB

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