A call to

  javax.xml.parsers.DocumentBuilderFactory.setFeature(
      "http://apache.org/xml/features/validation/dynamic", true);

causes the following exception at runtime:

  javax.xml.parsers.ParserConfigurationException:
  jaxp_feature_not_supported: Feature
  "http://apache.org/xml/features/validation/dynamic" is not supported.
 
In an environment where an XML document may need to be validated against DTDs or schemas, the lack of support for this feature requires any document that needs to be validated against a DTD to be parsed twice: The first time in order to determine whether the XML document references a DTD or schema, and the second time to parse it with DTD validation enabled, by calling "setValidating(true)" on the DocumentBuilderFactory.