Yoy может передать вам собственную реализацию DefaultHandler:
...SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
saxParser.parse(InputSource, new Defaulthandler() {
@Override
public InputSource resolveEntity(String publicId, String systemId)
throws IOException, SAXException {
InputStream is = ClassLoader.getSystemResourceAsStream("path_to_you_local_dtd_doc");
return is != null ? new InputSource(is) :
super.resolveEntity(publicId, systemId);
}
} )