How do I validate XML against a DTD (.dtd) - not a schema (.xsd) - using Java 5?

I'm used JAXB to generate some Java classes, which I now use as part
of a web service. Now, I'd like to validate the XML requests that are
coming into my web service. I read this is possible using the
validators and whatnot, but many API's since Java 5 are deprecated,
including most of the 'isValidating()'-related APIs. I also tried to
use the 'ValidationEventCollector' class with the unmarshaller, but it
doesn't actually do anything except take up lines of code.

        ValidationEventCollector vec = new ValidationEventCollector();
        u.setEventHandler( vec );

        Object obj = u.unmarshal( new StreamSource( new StringReader(
xmlStr.toString() ) ) );

        if ( vec.hasEvents() ){
            ValidationEvent[] validationEvents = vec.getEvents();
            
            System.out.println("There are validation events...");
            for (ValidationEvent ve : validationEvents){
                int errorLevel = ve.getSeverity();
                if ( errorLevel==ValidationEvent.ERROR ||
errorLevel==ValidationEvent.FATAL_ERROR ){
                    System.out.println("Error or Fatal event..." + ve);
                }
                else {
                    System.out.println("Warning event: " + ve);
                }
            }



Sun has a validation example using a schema (.xsd). I want to use a DTD. The
Sun example is below
(http://java.sun.com/j2se/1.5.0/docs/api/javax/xml/validation/package-summary.html):

 // parse an XML document into a DOM tree
    DocumentBuilder parser =
DocumentBuilderFactory.newInstance().newDocumentBuilder();
    Document document = parser.parse(new File("instance.xml"));

    // create a SchemaFactory capable of understanding WXS schemas
    SchemaFactory factory =
SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

    // load a WXS schema, represented by a Schema instance
    Source schemaFile = new StreamSource(new File("mySchema.xsd"));
    Schema schema = factory.newSchema(schemaFile);

    // create a Validator instance, which can be used to validate an
instance document
    Validator validator = schema.newValidator();

    // validate the DOM tree
    try {
        validator.validate(new DOMSource(document));
    } catch (SAXException e) {
        // instance document is invalid!
    }

If you execute this code above and replace 'mySchema.xsd' with a DTD
with the same rules (make it very simple, of course), then you'll
start getting some of the errors I've been getting. On that same Sun
page, there is also a long note about how DTDs are intricately linked
to parsing and how if you try to do one without the other the Sun will
melt and we'll all die. I don't know what it means.

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