getting more informations from sax validator

Question

Can i get for example the node structure or something like this from the validator? Something like a listener or an handler. The exception is not enough. I have to select the node where the error occured. Thats what i build so far.

def factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI)
def schema = factory.newSchema(new StreamSource(new FileReader("src/import.xsd")))
def validator = schema.newValidator()
try {
    validator.validate(new StreamSource(new FileReader("src/import.xml")))
    println "everything is fine"
} catch(SAXException e) {   
    println e
}

Thank you.

Answer 1

Validate when you parse. Here's the code in Java, looks like the translation to Groovy should be pretty straightforward:

InputStream xml = // …
InputStream xsd = // …

SchemaFactory xsFact = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = xsFact.newSchema(new StreamSource(xsd));

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
dbf.setValidating(false);
dbf.setSchema(schema);
DocumentBuilder db = dbf.newDocumentBuilder();

Document dom = db.parse(new InputSource(xml));

Answer 2

You have to use the SAXParseException to get more errors or the SAX locator if you're implementing ContentHandler, and possibly a lexer. The exception will give you details about the error, line number.

try{
  ...
}
catch(SAXParseException e){
   int lineNumber = e.getLineNumber();
   int columnNumber = e.getColumnNumber();
   String message = e.getMessage();
   // do something
}
catch(SAXException e){
   // what should we do?
   // if we're implementing ContentHandler 
   // we can use the org.xml.sax.Locator to get more info
}

Usually the column information from the Locator returns -1. For offset precision, you'll have to either use an extended ContentHandler or a lexer:

• Get the line number of the error
• Estimate the position of the node with the line information, attributes(start tag, end tag) using a lexer or regular expressions or something else.

Answer 3

Depending on how much control you have over the environment, there is a somewhat clunky way to do this. The Xerxes 2 XML parser, which is a drop-in replacement for the default parser, has a property on the Validator to get the current node, so if you keep a reference to the Validator (as a field of an ErrorHandler that you set on the Validator, for example) you can get the node structure. Here's how I did it in Java:

...
  Validator validator = schema.newValidator();
  validator.setErrorHandler(new MyErrorHandler(validator));
...



public class MyErrorHandler implements ErrorHandler {
  private Validator validator;

  public AnnotatingErrorHandler(Validator v) {
    super();
    validator = v;
  }

  @Override
  public void error(SAXParseException e) throws SAXException {

    try {
      element = (Element)validator.getProperty("http://apache.org/xml/properties/dom/current-element-node");
    } catch (SAXNotRecognizedException e) {
      log(Level.SEVERE, "Xerxes 2 XML parser is required", saxnre);
    } catch (SAXNotSupportedException e) {
   ; // shouldn't happen in this context
    }
    ... // do stuff
  }
  ...
}

Answer 4

Came across the same issue and resolved it by using the following.

1. Used SAXSource when using the validate method.
2. Used Implementation of error handler to capture SAXParseException.