Reference links:
https://examples.javacodegeeks.com/core-java/xml/java-xml-parser-tutorial/
https://www.mkyong.com/java/how-to-read-xml-file-in-java-dom-parser/
The code : https://github.com/dianaplazar10/JAVAproject.git
An XML document consists of elements. Each element has a start tag, its content and an end tag. Also, an XML document must have exactly one root element.
In java, there are 3 ways of parsing an XML:
1) DOM parser :
The DOM(Document Object Model) parser parses the entire XML document and loads the XML content into a Tree structure. Using the and classes, we can retrieve and modify the content of an XML file.
Inside the main method, we
- create a from the and then,
- parse and store the XML file in an instance of the class.
- Then, we parse that document and when we find a node of type ,
- we retrieve all its information and store them in an instance of the Employee class.
- Finally, we print the information of all stored employees.
- APIs used: DocumentBuilder, Document, NodeList, Node, Element
2) SAX parser :
SAX(event-based Sequential Access parser API) parser only needs to report each parsing event as it happens and the minimum memory required for a SAX parser is proportional to the maximum depth of the XML file.
startElement: this event is triggered when a start tag is encountered.
endElement: – this event is triggered when an end tag is encountered.
characters: – this event is triggered when some text data is encountered.
3) StAX parser :
StAX(Streaming API for XML)parser is able to process tree-like structured data as the data gets streamed-in. StAX was designed as a median between DOM and SAX parsers. In this parsing, the entry point is a cursor that represents a point within the XML document. The application moves the cursor forward, in order to pull the information from the parser. In contrast, a SAX parser pushes data to the application, instead of pulling.
Examples:
1) DOM parser
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package com.soap.xmlParse;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
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.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class DomParserExample {
public static void main(String[] args) throws ParserConfigurationException,
SAXException, IOException {
if(args.length != 1)
throw new RuntimeException("The name of the XML file is required!");
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
// Load the input XML document, parse it and return an instance of the
// Document class.
Document document = builder.parse(new File(args[0]));
List<Employee> employees = new ArrayList<Employee>();
NodeList nodeList = document.getDocumentElement().getChildNodes();
for (int i = 0; i < nodeList.getLength(); i++) {
Node node = nodeList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
Element elem = (Element) node;
String ID = node.getAttributes().getNamedItem("ID").getNodeValue(); // Get the value of the ID attribute.
// Get the value of all sub-elements.
String firstname = elem.getElementsByTagName("Firstname").item(0).getChildNodes().item(0).getNodeValue();
String lastname = elem.getElementsByTagName("Lastname").item(0).getChildNodes().item(0).getNodeValue();
Integer age = Integer.parseInt(elem.getElementsByTagName("Age").item(0).getChildNodes().item(0).getNodeValue());
Double salary = Double.parseDouble(elem.getElementsByTagName("Salary").item(0).getChildNodes().item(0).getNodeValue());
employees.add(new Employee(ID, firstname, lastname, age, salary));
}
}
// Print all employees.
for (Employee empl : employees)
System.out.println(empl.toString());
}
}
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2) SAX parser
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package com.soap.xmlParse;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class SAXParserExample extends DefaultHandler {
private static List<Employee> employees = new ArrayList<Employee>();
private static Employee empl = null;
private static String text = null;
@Override
// A start tag is encountered.
public void startElement(String uri, String localName, String qName, Attributes attributes)
throws SAXException {
switch (qName) {
// Create a new Employee.
case "Employee": {
empl = new Employee();//attributes.getValue("ID"), "Firstname", "Lastname", 33, 4000);
empl.setID(attributes.getValue("ID"));
break;
}
}
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
switch (qName) {
case "Employee": {
// The end tag of an employee was encountered, so add the employee to the list.
employees.add(empl);
break;
}
case "Firstname": {
empl.setFirstname(text);
break;
}
case "Lastname": {
empl.setLastname(text);
break;
}
case "Age": {
empl.setAge(Integer.parseInt(text));
break;
}
case "Salary": {
empl.setSalary(Double.parseDouble(text));
break;
}
}
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
text = String.copyValueOf(ch, start, length).trim();
System.out.println(text + ":" + ch.toString() + ":" + start + ":" + length);
}
public static void main(String[] args) throws ParserConfigurationException,
SAXException, IOException {
if (args.length != 1)
throw new RuntimeException("The name of the XML file is required!");
SAXParserFactory parserFactor = SAXParserFactory.newInstance();
SAXParser parser = parserFactor.newSAXParser();
SAXParserExample handler = new SAXParserExample();
parser.parse(new File(args[0]), handler);
// Print all employees.
for (Employee empl : employees)
System.out.println(empl.toString());
}
}
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3) StAX parser
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package com.soap.xmlParse;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
public class StaxParserExample {
public static void main(String[] args) throws FileNotFoundException,
XMLStreamException {
if (args.length != 1)
throw new RuntimeException("The name of the XML file is required!");
List<Employee> employees = null;
Employee empl = null;
String text = null;
XMLInputFactory factory = XMLInputFactory.newInstance();
XMLStreamReader reader = factory.createXMLStreamReader(new FileInputStream(
new File(args[0])));
while (reader.hasNext()) {
int Event = reader.next();
switch (Event) {
case XMLStreamConstants.START_ELEMENT: {
if ("Employee".equals(reader.getLocalName())) {
empl = new Employee();
empl.setID(reader.getAttributeValue(0));
}
if ("Employees".equals(reader.getLocalName()))
employees = new ArrayList<>();
break;
}
case XMLStreamConstants.CHARACTERS: {
text = reader.getText().trim();
break;
}
case XMLStreamConstants.END_ELEMENT: {
switch (reader.getLocalName()) {
case "Employee": {
employees.add(empl);
break;
}
case "Firstname": {
empl.setFirstname(text);
break;
}
case "Lastname": {
empl.setLastname(text);
break;
}
case "Age": {
empl.setAge(Integer.parseInt(text));
break;
}
case "Salary": {
empl.setSalary(Double.parseDouble(text));
break;
}
}
break;
}
}
}
// Print all employees.
for (Employee employee : employees)
System.out.println(employee.toString());
}
}
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