Using JDOM to Parse XML file with external DTD that has not been declared in the XML file

Question

In my XML file I have some entities such as ’

So I have created a DTD tag for my XML document to define these entities. Below is the Java code used to read the XML file.

SAXBuilder builder = new SAXBuilder();
URL url = new URL("http://127.0.0.1:8080/sample/subject.xml");        
InputStream stream = url.openStream();
org.jdom.Document document = builder.build(stream);

Element root = document.getRootElement();

Element name = root.getChild("name");
result = name.getText();
System.err.println(result);

How can I change the Java code to retrieve a DTD over HTTP to allow the parsing of my XML document to be error free?

Simplified example of the xml document.

<main>
  <name>hello &lsquo; world &rsquo; foo  &amp; bar </name> 
</main>

Answer 1

One way to do this would be to read the document and then validate it with the transformer:

import java.net.URL;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

public class ValidateWithExternalDTD {
    private static final String URL = "http://127.0.0.1:8080/sample/subject.xml";
    private static final String DTD = "http://127.0.0.1/YourDTD.dtd";

    public static void main(String args[]) {
        try {
            DocumentBuilderFactory factory=                   DocumentBuilderFactory.newInstance();
            factory.setValidating(true);
            DocumentBuilder builder = factory.newDocumentBuilder();

            // Set the error handler
            builder.setErrorHandler(new org.xml.sax.ErrorHandler() {                
                public void fatalError(SAXParseException spex)
                        throws SAXException {
                    // output error and exit
                    spex.printStackTrace();
                    System.exit(0);
                }

                public void error(SAXParseException spex)
                        throws SAXParseException {
                    // output error and continue
                    spex.printStackTrace();
                }

                public void warning(SAXParseException spex)
                        throws SAXParseException {
                    // output warning and continue
                    spex.printStackTrace();
                }
            });

            // Read the document
            URL url = new URL(ValidateWithExternalDTD.URL);
            Document xmlDocument = builder.parse(url.openStream());
            DOMSource source = new DOMSource(xmlDocument);

            // Use the tranformer to validate the document
            StreamResult result = new StreamResult(System.out);                     
            TransformerFactory tf = TransformerFactory.newInstance();
            Transformer transformer = tf.newTransformer();
            transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, ValidateWithExternalDTD.DTD);
            transformer.transform(source, result);

            // Process your document if everything is OK
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

Another way would be to replace the XML title with the XML title plus the DTD reference

Replace this:

<?xml version = "1.0"?>

with this:

<?xml version = "1.0"?><!DOCTYPE ...>

Of course you would replace the first occurance only and not try to go through the whole xml document

You have to instantiate the SAXBuilder by passing true(validate) to its constructor:

SAXBuilder builder = new SAXBuilder(true);

or call:

builder.setValidation(true)