SaxParseException in XSD validation does not give element name

Question

I have an xsd file and an xml file, I am validating the xml file against the xsd file using the following code

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setValidating(true);
        factory.setAttribute(
                "http://java.sun.com/xml/jaxp/properties/schemaLanguage",
                "http://www.w3.org/2001/XMLSchema");
        factory.setAttribute(
                "http://java.sun.com/xml/jaxp/properties/schemaSource",
                new InputSource(new StringReader(xsd)));
        Document doc = null;
        try {
            DocumentBuilder parser = factory.newDocumentBuilder();
            MyErrorHandler errorHandler = new MyErrorHandler();
            parser.setErrorHandler(errorHandler);
            doc = parser.parse(new InputSource(new StringReader(xml))); 
            return true;
        } catch (ParserConfigurationException e) {
            System.out.println("Parser not configured: " + e.getMessage());
        } catch (SAXException e) {
            System.out.print("Parsing XML failed due to a "
                    + e.getClass().getName() + ":");
            System.out.println(e.getMessage());
        } catch (IOException e) {
            System.out.println("IOException thrown");
            e.printStackTrace();
        }
        return false;

MyErrorHanlder is

private static class MyErrorHandler implements ErrorHandler {
        public void warning(SAXParseException spe) throws SAXException {
            System.out.println("Warning: " + spe.getMessage() + " getColumnNumber is " + spe.getColumnNumber() + " getLineNumber " + spe.getLineNumber() + " getPublicId " + spe.getPublicId() + " getSystemId " + spe.getSystemId());
        }

        public void error(SAXParseException spe) throws SAXException {
            System.out.println("Error: " + spe.getMessage() + " getColumnNumber is " + spe.getColumnNumber() + " getLineNumber " + spe.getLineNumber() + " getPublicId " + spe.getPublicId() + " getSystemId " + spe.getSystemId());
            throw new SAXException("Error: " + spe.getMessage());
        }

        public void fatalError(SAXParseException spe) throws SAXException {
            System.out.println("Fatal Error:  " + spe.getMessage() + " getColumnNumber is " + spe.getColumnNumber() + " getLineNumber " + spe.getLineNumber() + " getPublicId " + spe.getPublicId() + " getSystemId " + spe.getSystemId());
            throw new SAXException("Fatal Error: " + spe.getMessage());
        }
    }

And when the xml does not comply with xsd I get an exception.. but this exception does not have the name of the xsd element due to which this error has occured .. The message looks like

Parsing XML failed due to a org.xml.sax.SAXException:Error: cvc-minLength-valid: Value '' with length = '0' is not facet-valid with respect to minLength '1' for type 'null'.

Instead of printing the name of the xsd element, the error message just has ''. Because of this I am not able to find and display(to the user) the exact element which is causing the error.

My xsd element looks like this

<xs:element name="FullName_FirstName">
    <xs:annotation>
        <xs:appinfo>
            <ie:label>First Name</ie:label>
            <ie:html_element>0</ie:html_element>
        </xs:appinfo>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:string">
            <xs:minLength value="1"/>
        </xs:restriction>
    </xs:simpleType>
</xs:element>

Thanks in advance

Answer 1

First of all, some advice. You don't need to build a DOM document just to do validation. This causes a large amount of memory overhead, maybe even running out on large input XML documents. You could just use a SAXParser. If you're using Java 1.5 or later, that isn't even necessary. From that version on, an XML validation API was included in Java SE. Check package javax.xml.validation for more info. The idea is that you first build a Schema object, then obtain a Validator from that which can be used to do validation. It accepts any Source implementation for input. Validators can also be given ErrorHandlers, so you can just reuse your class. Of course, it is possible that you actually will need a DOM, but in that case it's still better to make a Schema instance and register that with your DocumentBuilderFactory.

Now, for the actual problem. This isn't entirely easy, since the SAXParseException doesn't provide you with much context information. Your best bet is to have a ContentHandler hooked up somewhere and keep track of what element you're in, or some other positional information. You could then have that given to the error handler when needed. The class DefaultHandler or DefaultHandler2 is a convenient way of combining both error and content handling. You'll find those classes in package org.xml.sax.ext.

I've put together a test that I'll post below. Now, I do get two lines of output instead of the expected one. If this is because I'm using a Schema, or because I'm not throwing an exception and keep on processing, I'm not certain. The second line does contain the name of the element, so that might be enough. You could have some flag set on errors instead of throwing an exception and ending the parsing.

package jaxb.test;

import java.io.StringReader;
import javax.xml.XMLConstants;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;

public class ValidationTest {

    public static void main(String[] args) throws Exception {

        //Test XML and schema
        final String xml = "<?xml version=\"1.0\"?><test><test2></test2></test>";
        final String schemaString =
            "<?xml version=\"1.0\"?>"
            + "<xsd:schema xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" elementFormDefault=\"unqualified\" attributeFormDefault=\"unqualified\">"
            + "<xsd:element name=\"test\" type=\"Test\"/>"
            + "<xsd:element name=\"test2\" type=\"Test2\"/>"
            + "<xsd:complexType name=\"Test\">"
            + "<xsd:sequence>"
            + "<xsd:element ref=\"test2\" minOccurs=\"1\" maxOccurs=\"unbounded\"/>"
            + "</xsd:sequence>"
            + "</xsd:complexType>"
            + "<xsd:simpleType name=\"Test2\">"
            + "<xsd:restriction base=\"xsd:string\"><xsd:minLength value=\"1\"/></xsd:restriction>"
            + "</xsd:simpleType>"
            + "</xsd:schema>";

        //Building a Schema instance
        final Source schemaSource =
            new StreamSource(new StringReader(schemaString));
        final Schema schema =
            SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI).newSchema(schemaSource);

        //Creating a SAXParser for our input XML
        //First the factory
        final SAXParserFactory factory = SAXParserFactory.newInstance();
        //Must be namespace aware to receive element names
        factory.setNamespaceAware(true);
        //Setting the Schema for validation
        factory.setSchema(schema);
        //Now the parser itself
        final SAXParser parser = factory.newSAXParser();

        //Creating an instance of our special handler
        final MyContentHandler handler = new MyContentHandler();

        //Parsing
        parser.parse(new InputSource(new StringReader(xml)), handler);

    }

    private static class MyContentHandler extends DefaultHandler {

        private String element = "";

        @Override
        public void startElement(String uri, String localName, String qName,
                Attributes attributes) throws SAXException {

            if(localName != null && !localName.isEmpty())
                element = localName;
            else
                element = qName;

        }

        @Override
        public void warning(SAXParseException exception) throws SAXException {
            System.out.println(element + ": " + exception.getMessage());
        }

        @Override
        public void error(SAXParseException exception) throws SAXException {
            System.out.println(element + ": " + exception.getMessage());
        }

        @Override
        public void fatalError(SAXParseException exception) throws SAXException {
            System.out.println(element + ": " + exception.getMessage());
        }

        public String getElement() {
            return element;
        }

    }

}

It's a bit rough, but you can work on from this to get what you need.