How to Read XML Files in Java?

Introduction

Today, we are going to learn about how to read XML files in java. Before, reading the XML Files let us learn about XML.

XML Files

The full form of XML is Extensive Markup Language. HTML(Hyper Text Markup Language) and XML look alike. But here in the XML the tags created are user defined. This is an easier way to store data. Most crucially, because the fundamental structure of XML is defined, the recipient can still understand the data whether you share or transmit it across platforms, whether locally or over the internet. This is because XML syntax is standardized.

Sample Structure of XML File

<tag1>
       <subtag1>
             <subsubtag1>
             </subsubtag1>
        </subtag1>
        <subtag2>
        </subtag2> 
</tag1> 
<tag2> 
</tag2>

Example XML Code

<?xml version="1.0"?>  
< class >  
    < student >  
        < id > 101 < / id >  
        < firstname > JOE < / firstname >  
        < lastname > ROOT < / lastname >  
        < number > 66 < / number >  
        < runs > 10458 < / runs >  
    < / student >  
 < / class >

Output

 101 
 JOE 
 ROOT 
 66 
 10458 

Example 2:

<?xml version="1.0"?>  
< India >  
    < medals >  
        < place > 4 < / place >  
        < gold > 21 < / golds >  
        < silver > 16 < / silver >  
        < bronze > 23 < / bronze >  
        < total > 61 < / total >  
    < / medals >  
 < / India >

Output

 4 
 21 
 16 
 23 
 61 

We will know more about the output while coding in java.

Difference between XML and HTML

XML	HTML
XML stands for Extensive Markup Language	HTML stands for Hyper Text Markup Language
User Defined tags are used here	Pre-defined tags are used here
XML does not allow errors	HTML ignores some errors
Case Sensitive	Not Case Sensitive
XML Tags are extensible	HTML Tags are not extensible
XML is dynamic in nature	HTML is static in nature
XML stores data	HTML displays data

Reading XML Files in Java

Reading XML files is not similar to reading of .txt, .py, etc. We require APIs for this task. The APIs are

• The SAX API
• The DOM API

DOM API

The classes to read and write an XML file are provided by the DOM API. Using the DOM API, we are able to create, remove, change, and rearrange the node. A DOM object is created in memory once the DOM parser fully processes the whole XML file. The node stands for one of an XML file's elements. When it loads an XML file into memory, the DOM parser takes a long time and uses a lot of memory.

XML Code

File Name: Players.xml

<?xml version="1.0"?>  
<class>  
    <student>  
        <number>66</number>  
        <firstname>Joe</firstname>  
        <lastname>Root</lastname>  
        <Team>England</Team>  
        <runs>10458</runs>  
    </student>  
      
    <student>  
        <number>18</number>  
        <firstname>Virat</firstname>  
        <lastname>Kohli</lastname>  
        <Team>India</Team>  
        <runs>8074</runs>  
    </student>  
  
    <student>  
        <number>11</number>  
        <firstname>Kumara</firstname>  
        <lastname>Sangakkara</lastname>  
        <Team>Sri Lanka</Team>  
        <runs>12400</runs>  
    </student> 
  
   <student>  
        <number>26</number>  
        <firstname>Alastair</firstname>  
        <lastname>Cook</lastname>  
        <Team>England</Team>  
        <runs>12472</runs>  
    </student>
 
   <student>  
        <number>19</number>  
        <firstname>RAHUL</firstname>  
        <lastname>DRAVID</lastname>  
        <Team>India</Team>  
        <runs>13288</runs>  
    </student>  
  
</class> 

Rules for writing XML Files

• XML Files are case sensitive
• White spaces are technically intended for inclusion of white spaces in the tags, elements, etc.
• All XML Tags must have a closing tag
• XML Files does not ignore errors, so, we have to be very careful
• Root elements are must for an XML File
• All XML Elements must be properly nested

This is how the XML file looks. Let us get the output of XML file by using DOM Parser.

Example Code:

File Name: DomAPI.java

// the program which uses DOM Parser to read the XML Files
import java.io.*;
import org.w3c.dom.Document;  
import org.w3c.dom.NodeList;  
import org.w3c.dom.Node;  
import org.w3c.dom.Element;  
import javax.xml.parsers.DocumentBuilderFactory;  
import javax.xml.parsers.DocumentBuilder;  


public class DomAPI  
{  
public static void main(String args [])   
{  
try   
{  


// creating an object for file class where the object contains the contents of the file


File file = new File("C:/new/D.xml");  


//an instance of factory that gives a document builder  


DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  


//an instance of builder  


DocumentBuilder db = dbf.newDocumentBuilder();  


// parsing the xml file
Document doc = db.parse(file);  


doc.getDocumentElement().normalize();  


System.out.println("Root element: " + doc.getDocumentElement().getNodeName());  


NodeList nodeList = doc.getElementsByTagName("student");  


// nodeList is used here


// nodeList cannot be iterated


//So are using for loop


for(int it = 0; it < nodeList.getLength(); it++)   


{  
Node node = nodeList.item(it);  


System.out.println("\nNode Name:" + node.getNodeName());  


if(node.getNodeType() == Node.ELEMENT_NODE)   


{  


Element e =(Element) node;  


System.out.println("Number:"
+e.getElementsByTagName("number").item(0).getTextContent());  


System.out.println("First Name:"
+e.getElementsByTagName("firstname").item(0).getTextContent());  


System.out.println("Last Name:"
+e.getElementsByTagName("lastname").item(0).getTextContent());  


System.out.println("Team: "+ e.getElementsByTagName("Team").item(0).getTextContent());  


System.out.println("Runs: "+ e.getElementsByTagName("runs").item(0).getTextContent());  
}  
}  
}   
catch(Exception ex)   
{  
ex.printStackTrace();  
}  
}  

Output:

C:\new>javac ReadXMLFileExample1.java


C:\new>java ReadXMLFileExample1
Root element: class


Node Name: student
Number: 66
First Name: Joe
Last Name: Root
Team: England
Runs: 10458


Node Name: student
Number: 18
First Name: Virat
Last Name: Kohli
Team: India
Runs: 8074


Node Name: student
Number: 11
First Name: Kumara
Last Name: Sangakkara
Team: Sri Lanka
Runs: 12400


Node Name: student
Number: 26
First Name: Alastair
Last Name: Cook
Team: England
Runs: 12472


Node Name: student
Number: 19
First Name: RAHUL
Last Name: DRAVID
Team: India
Runs: 13288


C:\new>

Note:

If the program is not working then download dom-2.3.0-jaxb-1.0.6.jar file.

SAX Parser

Simple API for XML is the name of the Java SAX parser. An XML file is parsed line by line by the SAX parser. When it comes across the opening tag, ending tag, and character data in an xml file, it starts events. The event-based parser is another name for the SAX parser.

Because SAX is a streaming interface for XML, XML files are parsed sequentially from the top of the page all the way down to the closure of the root element.

No XML files are loaded into memory by the SAX parser. The XML document's object representation is not created. Call back functions are used by the SAX parser to notify clients of the structure of the XML document. Compared to DOM parser, it is quicker and requires less memory.

Example XML File

File Name : D.xml

<?xml version="1.0"?>  
<class>  
    <student>  
        <number>66</number>  
        <firstname>Joe</firstname>  
        <lastname>Root</lastname>  
        <Team>England</Team>  
        <runs>10458</runs>  
    </student>  
      
    <student>  
        <number>18</number>  
        <firstname>Virat</firstname>  
        <lastname>Kohli</lastname>  
        <Team>India</Team>  
        <runs>8074</runs>  
    </student>  
  
    <student>  
        <number>11</number>  
        <firstname>Kumara</firstname>  
        <lastname>Sangakkara</lastname>  
        <Team>Sri Lanka</Team>  
        <runs>12400</runs>  
    </student> 
  
   <student>  
        <number>26</number>  
        <firstname>Alastair</firstname>  
        <lastname>Cook</lastname>  
        <Team>England</Team>  
        <runs>12472</runs>  
    </student>
 
   <student>  
        <number>19</number>  
        <firstname>RAHUL</firstname>  
        <lastname>DRAVID</lastname>  
        <Team>India</Team>  
        <runs>13288</runs>  
    </student>  
  
</class>

Example Java Program

File Name: SaxAPi.java

// Using SAX Parser
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 ReadXMLFileExample3  
{  
public static void main(String args[])   
{  
try   
{  
SAXParserFactory factory = SAXParserFactory.newInstance();  
SAXParser saxParser = factory.newSAXParser();  
DefaultHandler handler = new DefaultHandler()   
{  
boolean number = false;  
boolean firstname = false;  
boolean lastname = false;  
boolean team = false;  
boolean runs = false;  
//parser starts parsing a specific element inside the document    
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException   
{  
System.out.println("\nStart Element :" + qName);  
if(qName.equalsIgnoreCase("number"))  
{  
number=true;  
}  
if(qName.equalsIgnoreCase("firstname"))   
{  
firstname = true;  
}  
if(qName.equalsIgnoreCase("lastname"))   
{  
lastname = true;  
}  
if(qName.equalsIgnoreCase("Team"))   
{  
team = true;  
}  
if(qName.equalsIgnoreCase("runs"))   
{  
runs = true;  
}  
}  
//parser ends parsing the specific element inside the document  
public void endElement(String uri, String localName, String qName) throws SAXException   
{  
System.out.println("\nEnd Element:" + qName);  
}  
//reads the text value of the currently parsed element  
public void characters(char ch[], int start, int length) throws SAXException   
{  
if(number)   
{  
System.out.println("Number : " + new String(ch, start, length));  
number = false;  
}  
if(firstname)   
{  
System.out.println("First Name: " + new String(ch, start, length));  
firstname = false;  
}  
if(lastname)   
{  
System.out.println("Last Name: " + new String(ch, start, length));  
lastname = false;  
}  
if(team)  
{  
System.out.println("Team: " + new String(ch, start, length));  
team = false;  
}  
if(runs)   
{  
System.out.println("Runs : " + new String(ch, start, length));  
runs = false;  


}
  
}  
 
};  
saxParser.parse("C:/new/D.xml", handler);  
}
  
catch(Exception e)   
{  
e.printStackTrace();  
}


}  

Output:

C:\new>javac ReadXMLFileExample3.java


C:\new>java ReadXMLFileExample3


Start Element: class


Start Element: student


Start Element: number
Number: 66


End Element: number


Start Element :firstname
First Name: Joe


End Element: firstname


Start Element :lastname
Last Name: Root


End Element:lastname


Start Element :Team
Team: England


End Element: Team


Start Element :runs
Runs : 10458


End Element: runs


End Element: student


Start Element :student


Start Element :number
Number : 18


End Element: number


Start Element :firstname
First Name: Virat


End Element: firstname


Start Element :last name
Last Name: Kohli


End Element:lastname


Start Element :Team
Team: India


End Element: Team


Start Element :runs
Runs : 8074


End Element: runs


End Element: student


Start Element :student


Start Element :number
Number : 11


End Element: number


Start Element :firstname
First Name: Kumara


End Element: firstname


Start Element :lastname
Last Name: Sangakkara


End Element: lastname


Start Element: Team
Team: Sri Lanka


End Element: Team


Start Element :runs
Runs : 12400


End Element: runs


End Element: student


Start Element :student


Start Element :number
Number : 26


End Element: number


Start Element :firstname
First Name: Alastair


End Element: firstname


Start Element :lastname
Last Name: Cook


End Element: lastname


Start Element :Team
Team: England


End Element: Team


Start Element :runs
Runs : 12472


End Element: runs


End Element: student


Start Element :student


Start Element :number
Number : 19


End Element: number


Start Element :firstname
First Name: RAHUL


End Element: firstname


Start Element :lastname
Last Name: DRAVID


End Element: lastname


Start Element :Team
Team: India


End Element: Team


Start Element :runs
Runs : 13288


End Element: runs


End Element: student


End Element: class


C:\new>