Essential XML: Beyond Markup

SAX Error Handling

Most SAX interface methods throw SAXException. SAXException extends java.lang.Exception and adds one fundamental feature, which is the ability to piggyback an arbitrary exception inside of a SAXException. This allows implementations to propagate non-SAX-related exceptions across SAX interface method boundaries. Consider the following implementation of ContentHandler.characters:

void characters(char[] ch, int offset, int length)
                    throws org.xml.sax.SAXException {
  try {
    this.out.write(ch, offset, length);
  }
  catch (java.io.IOException ex) {
    throw new org.xml.sax.SAXException(ex);
  }
}

This implementation embeds a java.io.IOException inside the SAXException that it is required to throw. Callers can then scrape out the exception ...