Spring MappingJackson2HttpMessageConverter not getting triggered?

Question

I have a fairly old Java 8 / Spring app which provides a REST API. The response is sent in either JSON or XML depending on the Accept Header.

So for example

• application/json-v1 converts the response to JSON of version 1 of the response object
• application/json-v2 - converts the response to JSON of version 1 of the response object
• application/xml-v1 - converts the response to XML of version 1 of the response object

The app is in Spring 5 now but was initially in Spring3 and this aspect has never been converted to use code config.

So the core config XML is has this

<!-- Enables the Spring MVC @Controller programming model, and set converters in use -->
    <mvc:annotation-driven>
        <message-converters>
            <beans:bean class="com.packagpath.AppJaxb2RootElementHttpMessageConverter">
                <beans:property name="supportedMediaTypes">
                    <beans:list>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="xml"/>
                        </beans:bean>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="xml-v1"/>
                        </beans:bean>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="xml-v2"/>
                        </beans:bean>
                    </beans:list>
                </beans:property>
            </beans:bean>

            <beans:bean class="com.packagpath.AppMappingJackson2HttpMessageConverter">
                <beans:property name="supportedMediaTypes">
                    <beans:list>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="json"/>
                        </beans:bean>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="json-v1"/>
                        </beans:bean>
                        <beans:bean class="org.springframework.http.MediaType">
                            <beans:constructor-arg index="0" value="application"/>
                            <beans:constructor-arg index="1" value="json-v2"/>
                        </beans:bean>
                    </beans:list>
                </beans:property>
            </beans:bean>
            <beans:bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
        </message-converters>
    </mvc:annotation-driven>

    <beans:bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
    </beans:bean>

The controllers have the produces attribute set along these lines

@RequestMapping(method = RequestMethod.GET, value = AppController.RESOURCE_NAME + "/{id}", produces = {
            XML_MIME_TYPE_DEFAULT, JSON_MIME_TYPE_DEFAULT, XML_MIME_TYPE_V1, JSON_MIME_TYPE_V1,
            XML_MIME_TYPE_V2, JSON_MIME_TYPE_V2 })
    @ResponseBody
    public Person getAccount(@PathVariable(value = "id") String id, HttpServletRequest request) { ...

The main override class for the JSON handler is along these lines...

public class AppMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
    private Utils utils = new Utils();

    /**
     * Init method must be called to ensure the object mapper used by this converter ignores null fields.
     */
    @PostConstruct
    public void init() {
        System.out.println("init 1");
        getObjectMapper().setSerializationInclusion(JsonInclude.Include.NON_NULL);
        System.out.println("init 2");

    }
//
    @Override
    protected void writeInternal(Object responseObject,  HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
        System.out.println("VersionConversion versionConversion");
    ...

So having set the scene. The XML version works well.

    public class AppJaxb2RootElementHttpMessageConverter extends Jaxb2RootElementHttpMessageConverter {
        private Utils utils = new Utils();

        @Override
        protected void writeToResult(Object responseObject, HttpHeaders headers, Result result) throws IOException {
            VersionConversion versionConversion = AnnotationUtils.findAnnotation(responseObject.getClass(), VersionConversion.class);
...

The basic config seems to work for the JSON message handler as if I put a configured Mime type in the header it returns a JSON document but if I put a non existent version it throws an error.

However the writeInternal method never gets called and so any version change code is never reached. I've looked at this from a few angles and I can't work out why. The clumsy Init 1, init2 print statements get output to the console. I'm sure it used to work but I can't see what is different now and as it is all wired in Spring I'm not sure how to investigate any further than looking at the code for errors!

If anyone knows what the issue might be that would be fantastic, at the moment though I'm not sure how & where to investigate as a) the code definitely used to work and b) I can't see anything wrong in the config that has changed. I'm wondering if it is a change in the dependencies that I didn't notice at the time ?