Re: NullPointerException handling

From:

Manivannan Palanichamy <manivannan.palanichamy@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 18 Aug 2007 06:00:22 -0000

Message-ID:

<1187416822.623402.116300@j4g2000prf.googlegroups.com>

On Aug 17, 4:18 am, ramu <ramu....@gmail.com> wrote:

i,
      I have the following code.

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.lang.NullPointerException npe)
                 {
                        System.out.println("NullPointerException
"+npe.getMessage());
                 }
                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;
                alidationError = 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){
                try{
                String SchemaUrl=argv[0];
                String XmlDocumentUrl=argv[1];
                SchemaValidator validator=new SchemaValidator();

                validator.validateSchema(SchemaUrl, XmlDocumentUrl);

                        } catch(java.lang.NullPointerException npe)
                        {

System.out.println("NullPointerException");
                        }
        }

Here XmlDocumentUrl is the xml document. Am trying to validating a xml
document(XmlDocumentUrl) with the schema specified by SchemaUrl. But
when I miss some attribute in the xml document(XmlDocumentUrl) its
throwing NullPointerException. After catching the NullPointerException
I want to handle it. I want to print an error message which specifies
in which file(XmlDocumentUrl) it occured and the line in that
file(XmlDocumentUrl). Can anyone tell me how to do this?

Why dont you add an if condition to check null values?
like,
if (xsdValidator == null)
throw new RuntimeException("xsdValidator is null.");

NullPointerExcetpion is something, an application is not supposed to
throw. Remember, every NullPointerException is considered to be a Bug
by many design principles. Applications should add null handles (like
if condition) and wrap it by a custom exception & then throw.

--
Manivannan Palanichamy
http://mani.gw.googlepages.com/index.html