∟DOMValidator.java - Validating XML with DTD using DOM
This section provides a tutorial example on how to use DOM API provided in JDK 1.4 to write a Java program to validate an XML document against the specified DTD document type.
J2SDK 1.4 offers a document builder interface, 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 you 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. http://www.herongyang.com/
*/
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"?>
<!-- invalid_dtd.xml
Copyright (c) 2002 by Dr. Herong Yang. http://www.herongyang.com/
-->
<!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>
Run the sample Java program, java DOMValidator invalid_dtd.xml, I got:
Error:
Public ID: null
System ID: file:C:/herong/invalid_dtd.xml
Line number: 24
Column number: -1
Message: Attribute "language" is not declared for element "name".
Error:
Public ID: null
System ID: file:C:/herong/invalid_dtd.xml
Line number: 30
Column number: -1
Message: Value "yes" is not one of the enumerated values
for this attribute.
Error:
Public ID: null
System ID: file:C:/herong/invalid_dtd.xml
Line number: 32
Column number: -1
Message: Element "word" does not allow "note" here.
Error:
Public ID: null
System ID: file:C:/herong/invalid_dtd.xml
Line number: 35
Column number: -1
Message: Attribute value for "date" is #REQUIRED.
Error:
Public ID: null
System ID: file:C:/herong/invalid_dtd.xml
Line number: 38
Column number: -1
Message: Element "definition" does not allow "i" -- (#PCDATA)
This is perfect. It tells you where the error is, and why it's an error.
