how can i unmarshall in jaxb and enjoy the schema

Question

I am using jaxb for my application configurations

I feel like I am doing something really crooked and I am looking for a way to not need an actual file or this transaction.

As you can see in code I:

1.create a schema into a file from my JaxbContext (from my class annotation actually) 2.set this schema file in order to allow true validation when I unmarshal

JAXBContext context = JAXBContext.newInstance(clazz);
Schema mySchema = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI).newSchema(schemaFile);
jaxbContext.generateSchema(new MySchemaOutputResolver()); // ultimately creates schemaFile   
Unmarshaller u = m_context.createUnmarshaller();
u.setSchema(mySchema);
u.unmarshal(...);

do any of you know how I can validate jaxb without needing to create a schema file that sits in my computer?

Do I need to create a schema for validation, it looks redundant when I get it by JaxbContect.generateSchema ?

How do you do this?

Answer 1

I had the exact issue and found a solution in the Apache Axis 2 source code:

protected List<DOMResult> generateJaxbSchemas(JAXBContext context) throws IOException {
    final List<DOMResult> results = new ArrayList<DOMResult>();
    context.generateSchema(new SchemaOutputResolver() {
        @Override
        public Result createOutput(String ns, String file) throws IOException {
            DOMResult result = new DOMResult();
            result.setSystemId(file);
            results.add(result);
            return result;
        }
     });
    return results;
}

and after you've acquired your list of DOMResults that represent the schemas, you will need to transform them into DOMSource objects before you can feed them into a schema generator. This second step might look something like this:

Unmarshaller u = myJAXBContext.createUnmarshaller();
List<DOMSource> dsList = new ArrayList<DOMSource>();   
for(DOMResult domresult : myDomList){
    dsList.add(new DOMSource(domresult.getNode()));
}
String schemaLang = "http://www.w3.org/2001/XMLSchema";
SchemaFactory sFactory = SchemaFactory.newInstance(schemaLang);
Schema schema = sFactory.newSchema((DOMSource[]) dsList.toArray(new DOMSource[0]));
u.setSchema(schema);            

Answer 2

If you use maven using jaxb2-maven-plugin can help you. It generates schemas in generate-resources phase.

Answer 3

I believe you just need to set a ValidationEventHandler on your unmarshaller. Something like this:

public class JAXBValidator extends ValidationEventCollector {
    @Override
    public boolean handleEvent(ValidationEvent event) {
        if (event.getSeverity() == event.ERROR ||
            event.getSeverity() == event.FATAL_ERROR)
        {
            ValidationEventLocator locator = event.getLocator();
            // change RuntimeException to something more appropriate
            throw new RuntimeException("XML Validation Exception:  " +
                event.getMessage() + " at row: " + locator.getLineNumber() +
                " column: " + locator.getColumnNumber());
        }

        return true;
    }
}

And in your code:

Unmarshaller u = m_context.createUnmarshaller();
u.setEventHandler(new JAXBValidator());
u.unmarshal(...);

Answer 4

Regarding ekeren's solution above, it's not a good idea to use PipedOutputStream/PipedInputStream in a single thread, lest you overflow the buffer and cause a deadlock. ByteArrayOutputStream/ByteArrayInputStream works, but if your JAXB classes generate multiple schemas (in different namespaces) you need multiple StreamSources.

I ended up with this:

JAXBContext jc = JAXBContext.newInstance(Something.class);
final List<ByteArrayOutputStream> outs = new ArrayList<ByteArrayOutputStream>();
jc.generateSchema(new SchemaOutputResolver(){
    @Override
    public Result createOutput(String namespaceUri, String suggestedFileName) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        outs.add(out);
        StreamResult streamResult = new StreamResult(out);
        streamResult.setSystemId("");
        return streamResult;
    }});
StreamSource[] sources = new StreamSource[outs.size()];
for (int i=0; i<outs.size(); i++) {
    ByteArrayOutputStream out = outs.get(i);
    // to examine schema: System.out.append(new String(out.toByteArray()));
    sources[i] = new StreamSource(new ByteArrayInputStream(out.toByteArray()),"");
}
SchemaFactory sf = SchemaFactory.newInstance( XMLConstants.W3C_XML_SCHEMA_NS_URI );
m.setSchema(sf.newSchema(sources));
m.marshal(docs, new DefaultHandler());  // performs the schema validation