how can i unmarshall in jaxb and enjoy the schema validation without using an explicit schema file

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 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 2

Found a way to do it, I am using Streams for creation of Schema and reading the schema.

JAXBContext context = JAXBContext.newInstance(clazz)
Unmarshaller u = context.createUnmarshaller(); 
final PipedInputStream in = new PipedInputStream();
context.generateSchema(new SchemaOutputResolver(){
  @Override
  public Result createOutput(String namespaceUri,   String suggestedFileName) throws IOException {
    StreamResult streamResult = new StreamResult(new PipedOutputStream(in));
    streamResult.setSystemId("");
    return streamResult;
  }});
u.setSchema(SchemaFactory.newInstance( XMLConstants.W3C_XML_SCHEMA_NS_URI ).newSchema(new StreamSource(in,"")));

The only thing I do not understand is what is the meaning of the set/getSystemId as you can see I am using blank String "".

Answer 3

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