DTD Validation in Java

Part:   1   2 

This tutorial describes:

• Validation with DOM
• Validation with SAX

Validation with DOM

J2SDK 1.4.1_01 offers a document builder interface, import javax.xml.parsers.DocumentBuilder, to represent classes that can parse XML files into document objects described in the Document Object Model (DOM). See my notes on DOM for more details.

The document builder also supports DTD validation during the parsing process. To do this:

• The document builder object must be set to validate DTD.
• You must create your own error handler class.
• The document builder object must be provided with an error handler object.

Here is a sample program, DOMValidator, that shows how to use a document builder class to validate XML files against the specified DTD statements.

/**
 * DOMValidator.java
 * Copyright (c) 2002 by Dr. Herong Yang
 */
import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.ErrorHandler;
import org.xml.sax.helpers.DefaultHandler;
class DOMValidator {
   public static void main(String[] args) {
      try {
      	 File x = new File(args[0]);
         DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
         f.setValidating(true); // Default is false
         DocumentBuilder b = f.newDocumentBuilder();
         // ErrorHandler h = new DefaultHandler();
         ErrorHandler h = new MyErrorHandler();
         b.setErrorHandler(h);
         Document d = b.parse(x);
      } 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 implements ErrorHandler {
      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());
      }
   }
}

To test DOMValidator, I created the following XML file with DTD statements, invalid_dtd.xml:

<?xml version="1.0"?>
<!-- dictionary_dtd.xml
     Copyright (c) 2002 by Dr. Herong Yang
-->
<!DOCTYPE dictionary [
 <!ELEMENT dictionary (note, word+)>
 <!ELEMENT note ANY>
 <!ELEMENT word (update?, name, definition+, usage*)>
 <!ELEMENT update EMPTY>
 <!ATTLIST update 
  date CDATA #REQUIRED 
  editor CDATA #IMPLIED
 >
 <!ELEMENT name (#PCDATA)>
 <!ATTLIST name is_acronym (true | false) "false">
 <!ELEMENT definition (#PCDATA)>
 <!ELEMENT usage (#PCDATA | i)*>
 <!ELEMENT i (#PCDATA)>
 <!ENTITY herong "Dr. Herong Yang">
]>
<dictionary>
 <note>Copyright (c) 2002 by &herong;</note>
 <word>
  <name is_acronym="true" language="EN">POP</name>
  <definition>Post Office Protocol</definition>
  <definition>Point Of Purchase</definition>
 </word>
 <word>
  <update date="2002-12-23"/> 
  <name is_acronym="yes">XML</name>
  <definition>eXtensible Markup Language</definition>
  <note>XML comes from SGML</note>
 </word>
 <word>
  <update editor="Herong Yang"/> 
  <name>markup</name>
  <definition>The amount added to the cost price to calculate 
the selling price - <i>Webster</i></definition>
 </word>
</dictionary>

(Continued on next part...)

Part:   1   2