web services - Server-Side XML Validation with CXF Webservice

Question

I'm working on an Apache CXF webservice (using JAX-WS, over SOAP). The service itself is pretty simple: receive a request, insert the request into a database, and return whether the insert was successful. I'd like to rely on XML validation to enforce a number of constraints on the request.

So, my question. How do I return detailed validation errors to a client of my service? I've turned validation on server-side by configuring my endpoint.

<jaxws:endpoint id="someEndpoint" implementor="#someImpl" address="/impl">
    <jaxws:properties>
        <!-- This entry should- ideally- enable JAXB validation
        on the server-side of our web service. -->
        <entry key="schema-validation-enabled" value="true" />
    </jaxws:properties>
</jaxws:endpoint>

I've explored using interceptors (eg BareInInterceptor) on the server, and somehow catching SAXParseExceptions to wrap them and send them along to the client. This approach seems a bit complicated, but I need to somehow give clients a line number if their XML is invalid. Should I go with interceptors to expose the exceptions?

I'm not very experienced with this technology stack, and just getting in to web services- any pointers you guys can give me would be really appreciated.

Answer 1

You can override validation error messages, inserting a line number, by using a custom ValidationEventHandler:

package example;

import javax.xml.bind.ValidationEvent;
import javax.xml.bind.helpers.DefaultValidationEventHandler;

public class MyValidationEventHandler extends DefaultValidationEventHandler {    
    @Override
    public boolean handleEvent(ValidationEvent event) {
        if (event.getSeverity() == ValidationEvent.WARNING) {
            return super.handleEvent(event);
        } else {
            throw new RuntimeException(event.getMessage()
                + " [line:"+event.getLocator().getLineNumber()+"]");
        }
    }
}

If you configure your endpoint to use this handler:

<jaxws:endpoint id="someEndpoint" implementor="#someImpl" address="/impl">
    <jaxws:properties>
        <entry key="schema-validation-enabled" value="true" />
        <entry key="jaxb-validation-event-handler">
            <bean class="example.MyValidationEventHandler" />
        </entry>
    </jaxws:properties>
</jaxws:endpoint>

Then you will get SOAP faults that look like this:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
    <soap:Body>
        <soap:Fault>
            <faultcode>soap:Client</faultcode>
            <faultstring>Unmarshalling Error: Not a number: xyz [line: 6]</faultstring>
        </soap:Fault>
    </soap:Body>
</soap:Envelope>

The jaxb-validation-event-handler property was only added to CXF pretty recently, so you need to make sure you're using the latest version - I tested this with 2.2.5.