Re: NullPointerException

From:

"Oliver Wong" <owong@castortech.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 7 Aug 2007 10:36:02 -0400

Message-ID:

<mr%ti.7163$VN1.96323@wagner.videotron.net>

"ramu" <ramu.ask@gmail.com> wrote in message
news:1186068383.230232.293360@x40g2000prg.googlegroups.com...

Hi,
    I want to validate an xml document against an XSD. The program is
written in java.
Below is the program:

package transform;

import oracle.xml.schemavalidator.XSDValidator;
import oracle.xml.parser.schema.XSDException;
import oracle.xml.parser.schema.XMLSchema;
import oracle.xml.parser.schema.XSDBuilder;
import oracle.xml.parser.v2.XMLError;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;
import java.net.URL;

public class SchemaValidator{

       public void validateSchema(String SchemaUrl, String
XmlDocumentUrl)
       {
               try {
                       XSDValidator xsdValidator=new XSDValidator();
                       XSDBuilder builder = new XSDBuilder();
                       URL url = new URL(SchemaUrl);
                       XMLSchema schemadoc =
(XMLSchema)builder.build(url);
                       xsdValidator.setSchema(schemadoc);

                       Validator handler=new Validator();
                       XMLError xmlError=new XMLError();
                       xmlError.setErrorHandler(handler);
                       xsdValidator.setError(xmlError);
                       xsdValidator.validate(new
URL(XmlDocumentUrl));
                       if(handler.validationError==true)
                               System.out.println("This XML Document
has Error: " + handler.saxParseException.getMessage());
                       else
                               System.out.println("This XML Document
is valid");

               }
               catch(java.io.IOException ioe)
               {
                       System.out.println("IOException
"+ioe.getMessage());
               }catch (SAXException e) {
                       System.out.println("SAXException
"+e.getMessage());
               }
               catch (XSDException e) {
                       System.out.println("SAXException
"+e.getMessage());
               }
       }

       private class Validator extends DefaultHandler{

               public boolean validationError = false;
               public SAXParseException saxParseException=null;

       public void error(SAXParseException exception) throws
SAXException{
               validationError = true;
               saxParseException=exception;
               }

               public void fatalError(SAXParseException exception)
throws SAXException{
           validationError = true;
           saxParseException=exception;
               }
               public void warning(SAXParseException exception)
throws SAXException{}

          }

       public static void main(String[] argv){
               String SchemaUrl=argv[0];
               String XmlDocumentUrl=argv[1];
               SchemaValidator validator=new SchemaValidator();
               validator.validateSchema(SchemaUrl, XmlDocumentUrl);

       }
}

When some attributes are missing in the XML document ,which is to be
validated, it is giving NullPointerException.

Exception in thread "main" java.lang.NullPointerException
       at oracle.xml.parser.v2.XMLError.flushNodes(XMLError.java:351)
       at
oracle.xml.parser.schema.XSDValidator.sendDOMError(XSDValidator.java:
1749)
       at
oracle.xml.parser.schema.XSDValidator.error(XSDValidator.java:1713)
       at
oracle.xml.parser.schema.XSDValidator.validateAttribute(XSDValidator.java:
671)
       at
oracle.xml.parser.schema.XSDValidator.startElement(XSDValidator.java:
534)
       at
oracle.xml.parser.v2.XMLElement.reportStartElement(XMLElement.java:
3066)
       at
oracle.xml.parser.v2.XMLElement.reportSAXEvents(XMLElement.java:2937)
       at
oracle.xml.parser.v2.XMLElement.reportChildSAXEvents(XMLElement.java:
2950)
       at
oracle.xml.parser.v2.XMLElement.reportSAXEvents(XMLElement.java:2939)
       at
oracle.xml.parser.v2.XMLElement.reportChildSAXEvents(XMLElement.java:
2950)
       at
oracle.xml.parser.v2.XMLElement.reportSAXEvents(XMLElement.java:2939)
       at
oracle.xml.parser.v2.XMLElement.reportChildSAXEvents(XMLElement.java:
2950)
       at
oracle.xml.parser.v2.XMLElement.reportSAXEvents(XMLElement.java:2939)
       at
oracle.xml.parser.v2.XMLElement.reportChildSAXEvents(XMLElement.java:
2950)
       at
oracle.xml.parser.v2.XMLDocument.reportSAXEvents(XMLDocument.java:
1389)
       at
oracle.xml.schemavalidator.XSDValidator.validate(XSDValidator.java:97)
       at
oracle.xml.schemavalidator.XSDValidator.validate(XSDValidator.java:
163)
       at
transform.SchemaValidator.validateSchema(SchemaValidator.java:28)
       at transform.SchemaValidator.main(SchemaValidator.java:68)

Instead of throwing NullPointerException, I want an proper error
message to be printed.
Can anyone please tell me how to do this?

    I haven't read the API for your oracle validator, but this feels like
a bug. You've got some sort of errorHandler which is set, so the least
surprising way for the library to behave to me would be for the
errorHandler to be invoked on the occurrence of a missing but required
attribute. Instead, the library is throwing a null pointer exception.

    Read the documentation to ensure that this is not the specified
behaviour (e.g. perhaps it says somewhere under what conditions NPE will
be thrown, and this is one of those conditions). If not, then report it as
a bug.

    - Oliver