Validate JAXBElement in JPA/JAX-RS Web Service

I have a JAX-RS webservice (Jersey) that is a CRUD interface for JPA (EclipseLink) entities. My entities were autogenerated from the database tables and I have annotated them with JAXB annotations so that they can be marshalled/unmarshalled to/from XML. My resource methods take JAXBElement objects as a parameter where required.

I don't have an XSD, however, I'm willing to write one to validate the XML received in the requests. But, I don't know how to initiate the validation. Jersey is automatically handling the marshalling/unmarshalling and any references I've found about validation is done at that level.

Does someone know of an example/tutorial that shows how to do this?

Thanks!

You could handle this by creating a custom MessageBodyReader. The example below is based on a Customer model:

import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.net.URL;

import javax.ws.rs.Consumes;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.ContextResolver;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.Provider;
import javax.ws.rs.ext.Providers;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;

@Provider
@Consumes("application/xml")
public class ValidatingReader implements MessageBodyReader<Customer> {

    @Context
    protected Providers providers;

    private Schema schema;

    public ValidatingReader() {
        try {
            SchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
            URL schemaURL = null;
            schema = sf.newSchema(schemaURL);
        } catch(Exception e) {
            throw new RuntimeException(e);
        }
    }

    public boolean isReadable(Class<?> arg0, Type arg1, Annotation[] arg2, MediaType arg3) {
        return arg0 == Customer.class;
    }

    public Customer readFrom(Class<Customer> arg0, Type arg1, Annotation[] arg2, MediaType arg3, MultivaluedMap<String, String> arg4, InputStream arg5)
            throws IOException, WebApplicationException {
        try {
            JAXBContext jaxbContext = null;
            ContextResolver<JAXBContext> resolver = providers.getContextResolver(JAXBContext.class, arg3);
            if(null != resolver) {
                jaxbContext = resolver.getContext(arg0);
            }
            if(null == jaxbContext) {
                jaxbContext = JAXBContext.newInstance(arg0);
            }
            Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
            unmarshaller.setSchema(schema);
            return (Customer) unmarshaller.unmarshal(arg5);
        } catch(JAXBException e) {
            throw new RuntimeException(e);
        }
    }

}

We can go one step further and create a generic (abstract) ValidatingReader which can be sub-classed as and when needed. This is what I've done, thanks to the idea from Blaise:

import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ContextResolver;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.Providers;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;

public abstract class AbstractValidatingReader<T> implements
    MessageBodyReader<T> {

@Context
protected Providers providers;

@SuppressWarnings("unchecked")
@Override
public boolean isReadable(Class<?> arg0, Type arg1, Annotation[] arg2,
        MediaType arg3) {

    Class<T> readableClass = (Class<T>) ((ParameterizedType) getClass()
            .getGenericSuperclass()).getActualTypeArguments()[0];
    return arg0 == readableClass;
}

@SuppressWarnings("unchecked")
@Override
public T readFrom(Class<T> arg0, Type arg1, Annotation[] arg2,
        MediaType arg3, MultivaluedMap<String, String> arg4,
        InputStream arg5) throws IOException, WebApplicationException {

    T type = null;
    JAXBContext jaxbContext = null;
    ContextResolver<JAXBContext> resolver = providers.getContextResolver(
            JAXBContext.class, arg3);
    try {

        if (resolver != null) {
            jaxbContext = resolver.getContext(arg0);
        }

        if (jaxbContext == null) {
            jaxbContext = JAXBContext.newInstance(arg0);

        }
        type = (T) jaxbContext.createUnmarshaller().unmarshal(arg5);
        validate(type);

    } catch (JAXBException e) {
        throw new WebApplicationException(
                Response.Status.INTERNAL_SERVER_ERROR);
    }

    return type;
}

protected abstract void validate(T arg0) throws WebApplicationException;
}

Override the validate method and annotate the sub-class with @Provider and we're done.