SAXValidator.java - XML DTD Validation with SAX

<< DTD (Document Type Definition) - XML Validation

<< JDK (Java Development Kit) Tutorials

This section provides a tutorial example on how to write a DTD validator using SAX classes in JDK. The validator can validate an XML file against the specified DTD statements.

Actually, SAX and DOM are sharing the same XML validation implementation. In this implementation, error events are fired during the parsing process. Application programs that are interested in validation errors must implement the error event handlers defined in the org.xml.sax.ErrorHandler interface.

In the SAX design, the ErrorHandler interface is integrated into the DefaultHandler class. Application programs just need to extend DefaultHandler and override those error event handlers.

Here is my SAX based XML validation program, SAXValidator.java:

/**
 * SAXValidator.java
 * Copyright (c) 2002 by Dr. Herong Yang
 */
import java.io.File;
import java.io.IOException;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.ParserConfigurationException;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;
class SAXValidator {
   public static void main(String[] args) {
      try {
      	 File x = new File(args[0]);
         SAXParserFactory f = SAXParserFactory.newInstance();
         f.setValidating(true); // Default is false         
         SAXParser p = f.newSAXParser();
         DefaultHandler h = new MyErrorHandler();
         p.parse(x,h);
      } catch (ParserConfigurationException e) {
         System.out.println(e.toString()); 
      } catch (SAXException e) {
         System.out.println(e.toString()); 
      } catch (IOException e) {
         System.out.println(e.toString()); 
      }
   }
   private static class MyErrorHandler extends DefaultHandler {
      public void warning(SAXParseException e) throws SAXException {
         System.out.println("Warning: "); 
         printInfo(e);
      }
      public void error(SAXParseException e) throws SAXException {
         System.out.println("Error: "); 
         printInfo(e);
      }
      public void fatalError(SAXParseException e) throws SAXException {
         System.out.println("Fattal error: "); 
         printInfo(e);
      }
      private void printInfo(SAXParseException e) {
        System.out.println("   Public ID: "+e.getPublicId());
        System.out.println("   System ID: "+e.getSystemId());
        System.out.println("   Line number: "+e.getLineNumber());
        System.out.println("   Column number: "+e.getColumnNumber());
        System.out.println("   Message: "+e.getMessage());
      }
   }
}

Note that:

• SAXParserFactory.setValidating(true) is called to turn on the validation funtion.
• The structure of this program is 99% identical to SAXBrowser.java. Since I am only interested the error events, only the error event handlers are overrode. If I copy the content event handlers here, and this program will be working as a browser and a validator at the same time.

Run "java SAXValidator invalid_dtd.xml", you will get the same output as DOMValidator.

Last update: 2006.

Sections in This Chapter

DOMValidator.java - XML DTD Validation with DOM

Testing DOM XML DTD Validator

SAXValidator.java - XML DTD Validation with SAX