steps to run dtds programs

Step 1: Create a New Java Project
Create a New Project:
Click on File > New > Java Project.
In the dialog that appears, enter a project name (e.g., XMLValidationProject).
Uncheck the option to create a module-info.java file if it appears.
Click Finish.
Step 2: Create the DTD and XML Files
Create a DTD File:
Right-click on the src folder in your new project in the Package Explorer.
Select New > File.
Name it 'customers.dtd' and click Finish.
Open customers.dtd and add the following content:
xml
<!ELEMENT customers (customer+)>
<!ELEMENT customer (name, email, phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

Create an XML File:
Right-click on the src folder again.
Select New > File.
Name it 'external_dtd.xml' and click Finish.
Open external_dtd.xml and add the following content:
xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE customers SYSTEM "customers.dtd">
<customers>
    <customer>
        <name>Satyam Nayak</name>
        <email>Satyam@nayak.com</email>
        <phone>122-112-1234</phone>
    </customer>
    <customer>
        <name>Sonu N</name>
        <email>Sonu@N.com</email>
        <phone>112-554-9969</phone>
    </customer>
</customers>

Step 3: Create the Java Files
Create a Simple Error Handler Class:
Right-click on the src folder.
Select New > Class.
Name it 'SimpleErrorHandler', and click Finish.
Add the following code to handle validation errors:
java
import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXParseException;

public class SimpleErrorHandler implements ErrorHandler {
    @Override
    public void warning(SAXParseException exception) throws SAXParseException {
        System.out.println("Warning: " + exception.getMessage());
    }

    @Override
    public void error(SAXParseException exception) throws SAXParseException {
        System.out.println("Error: " + exception.getMessage());
    }

    @Override
    public void fatalError(SAXParseException exception) throws SAXParseException {
        System.out.println("Fatal error: " + exception.getMessage());
    }
}

Create the Main Validation Class:
Right-click on the src folder.
Select New > Class.
Name it 'ValidateExternalDTD', and check the box to include the public static void main(String[] args) method, then click Finish.
Add the following code for XML validation:
java
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;

import java.io.File;
import java.io.IOException;

public class ValidateExternalDTD {
    public static void main(String[] args) {
        try {
            File xmlFile = new File("external_dtd.xml");
            DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
            dbFactory.setValidating(true); // Enable validation
            DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
            dBuilder.setErrorHandler(new SimpleErrorHandler());
            Document doc = dBuilder.parse(xmlFile);
            doc.getDocumentElement().normalize();
            System.out.println("XML is valid with External DTD.");
        } catch (ParserConfigurationException | SAXException | IOException e) {
            System.out.println("XML is invalid: " + e.getMessage());
        }
    }
}

Step 4: Run Your Program
Run the Program:
Right-click on the ValidateExternalDTD.java file in the Package Explorer.
Select Run As > Java Application.
View Output:
Check the Console view at the bottom of Eclipse for output messages indicating whether your XML is valid or invalid.