Spring Framework 4.1 ignores custom Object Mapper in ContentNegotiation - spring

Question

I'm trying to upgrade to Spring 4.1.5.
I have a custom Object mapper defined like so
<bean id="apiObjectMapper" class="my.company.ApiObjectMapper" />
<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager">
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper" ref="apiObjectMapper"/>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
The object mapper itself looks like this:
public class ApiObjectMapper extends ObjectMapper {
private static final long serialVersionUID = 1L;
public ApiObjectMapper() {
JaxbAnnotationModule module = new JaxbAnnotationModule();
module.setPriority(Priority.SECONDARY);
registerModule(module);
setSerializationInclusion(JsonInclude.Include.NON_NULL);
configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
}
}
The issue happens during content negotiation it seems
<bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
<property name="favorParameter" value="true" />
<property name="defaultContentType" value="text/xml" />
<property name="mediaTypes" >
<value>
json=application/json
xml=text/xml
</value>
</property>
</bean>
After upgrading, the object mapper is simply ignored. No Jaxb annotations are taken into account, NULLs appear.
Spring 4.0.9 works fine.
I tried Java Configuration with the same result.
Also tried configuring the new Jackson2ObjectMapperFactoryBean directly, but couldn't get the original behavior to happen either.
E.g.: Original output for an endpoint like "list.xml"
<result>
<typeB>
<itemA>...</itemA>
<itemB>...</itemB>
</typeB>
</result>
Now outputs (typeA is empty/null):
<result>
<typeA />
<typeB>
<itemA>...</itemA>
<itemB>...</itemB>
</typeB>
</result>
Any ideas?

Answer 1

I believe I found the culprit and fix for this issue.
When the content negotiation determines that the response should be serialized in JSON then org.springframework.http.converter.json.MappingJackson2HttpMessageConverter is used. However, if the response should be serialized in XML then org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter is used instead. Different message converter that will use a default object mapper if none is provided.
What I had to change was
public class ApiObjectMapper extends XmlMapper { // XmlMapper extends ObjectMapper
// same logic
}
and
<bean id="apiObjectMapper" class="my.company.ApiObjectMapper" />
<mvc:annotation-driven content-negotiation- manager="contentNegotiationManager">
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper" ref="apiObjectMapper"/>
</bean>
<!-- Added this bean configuration for XML serialization -->
<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter">
<property name="objectMapper" ref="apiObjectMapper"/>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
I have yet to find what changed in Spring Framework or Jackson to make this happen although my money is n the separation of Jackson XML handling into a different library (I'll update this answer once I do).
Hope it helps.

Answer 2

Leaving some more information for future reference.
Based on this Spring blog post, starting with Spring 4.1, Jackson XML is used to generate XML instead of Jaxb if the former is found on the classpath. That's the main reason for the output to change, because the library generating it changed.
Now after some trial and error, getting Jackson XML to generate the same output as Jaxb is quite the endeavour. Instead you could just remove all references to Jackson XML (not Jackson itself) and everything should work the same way it worked before.