Validation is a process of checking the source XML document to correspond to the DOCTYPE it referes. If the document corresponds to its doc-type it is calles valid, otherwise the document is invalid. In order to tell the SAX to check the document for validity a correspodning property of DOM-builderfactory should be set to true, like follows:

 // create new factory is ordinary way:
  DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

  // specifies that the builder produced by this factory will
  // validate documents as they are parsed.

  // this loader will validate XML-input:
  DocumentBuilder loader = factory.newDocumentBuilder();