XStreamMarshaller ignore unknown elements

Question

After change data model on server side my XStream client throw Exception

com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$UnknownFieldException: No such field {fieldName}

To prevent this behavior I try to do something to ignore unknown elements. I am using XStreamMarshaller from Spring-oxm 4.0.5 and XStream 1.4.5. I known that since XStream version 1.4.5 is available method ignoreUnknownElements().

XStreamMarshaller marshaller = new XStreamMarshaller();
    marshaller.setStreamDriver(streamDriver);
    marshaller.setAutodetectAnnotations(autodetectAnnotations);
    marshaller.getXStream().ignoreUnknownElements();

Above solution doesn't work and I still get mentioned exception.

I have client side model copied from server. For example:

public class Device implements Serializable {

    protected String device_id;

    protected String device_model_code;

    protected String device_model_name;

    protected String device_name;

//getters, setters
}

If I comment field for example device_model I will have Exception

com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$UnknownFieldException: No such field device_name

How can I solve my problem? How can I implement XStreamMarshaller to ignore unknown elements?

Answer 1

First thing is that method ignoreUnknownElements() available since XStream 1.4.5 is only for marshaling not for unmarshaling. So it doesn't work if somebody adds a new field in data model on server side.

To solve described problem you have to override protected method constructXStream() from org.springframework.oxm.xstream.XStreamMarshaller implementation:

public class CustomXStreamMarshaller extends XStreamMarshaller {

@Override
protected XStream constructXStream() {
    // The referenced XStream constructor has been deprecated as of 1.4.5.
    // We're preserving this call for broader XStream 1.4.x compatibility.
    return new XStream() {
        @Override
        protected MapperWrapper wrapMapper(MapperWrapper next) {
                return new MapperWrapper(next) {
                    @Override
                    public boolean shouldSerializeMember(Class definedIn, String fieldName) {
                        if (definedIn == Object.class) {
                            return false;
                        }
                        return super.shouldSerializeMember(definedIn, fieldName);
                    }
                };
        }
    };
}}

You only need to use your own implementation in XStreamMarshaller declaration:

CustomXStreamMarshaller marshaller = new CustomXStreamMarshaller();
    marshaller.setStreamDriver(streamDriver);
    marshaller.setAutodetectAnnotations(autodetectAnnotations);