This is NOT the ideal solution. See my second answer.
I solved this using a ModelAndViewResolver. You are able to register these directly with the AnnotationMethodHandlerAdapter with the perk of knowing that they'll always kick in first before the default handling occurs. Hence, Spring's documentation -
/**
* Set a custom ModelAndViewResolvers to use for special method return types.
* <p>Such a custom ModelAndViewResolver will kick in first, having a chance to resolve
* a return value before the standard ModelAndView handling kicks in.
*/
public void setCustomModelAndViewResolver(ModelAndViewResolver customModelAndViewResolver) {
this.customModelAndViewResolvers = new ModelAndViewResolver[] {customModelAndViewResolver};
}
Looking at the ModelAndViewResolver interface, I knew that it contained all the arguments needed to extend some functionality into how the handler method worked.
public interface ModelAndViewResolver {
ModelAndView UNRESOLVED = new ModelAndView();
ModelAndView resolveModelAndView(Method handlerMethod,
Class handlerType,
Object returnValue,
ExtendedModelMap implicitModel,
NativeWebRequest webRequest);
}
Look at all those delicious arguments in resolveModelAndView! I have access to virtually everything Spring knows about the request. Here's how I implemented the interface to act very similar to the MappingJacksonHttpMessageConverter except in a uni-directional manner (outward):
public class JsonModelAndViewResolver implements ModelAndViewResolver {
public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
public static final MediaType DEFAULT_MEDIA_TYPE = new MediaType("application", "json", DEFAULT_CHARSET);
private boolean prefixJson = false;
public void setPrefixJson(boolean prefixJson) {
this.prefixJson = prefixJson;
}
/**
* Converts Json.mixins() to a Map<Class, Class>
*
* @param jsonFilter Json annotation
* @return Map of Target -> Mixin classes
*/
protected Map<Class<?>, Class<?>> getMixins(Json jsonFilter) {
Map<Class<?>, Class<?>> mixins = new HashMap<Class<?>, Class<?>>();
if(jsonFilter != null) {
for(JsonMixin jsonMixin : jsonFilter.mixins()) {
mixins.put(jsonMixin.target(), jsonMixin.mixin());
}
}
return mixins;
}
@Override
public ModelAndView resolveModelAndView(Method handlerMethod, Class handlerType, Object returnValue, ExtendedModelMap implicitModel, NativeWebRequest webRequest) {
if(handlerMethod.getAnnotation(Json.class) != null) {
try {
HttpServletResponse httpResponse = webRequest.getNativeResponse(HttpServletResponse.class);
httpResponse.setContentType(DEFAULT_MEDIA_TYPE.toString());
OutputStream out = httpResponse.getOutputStream();
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setMixInAnnotations(getMixins(handlerMethod.getAnnotation(Json.class)));
JsonGenerator jsonGenerator =
objectMapper.getJsonFactory().createJsonGenerator(out, JsonEncoding.UTF8);
if (this.prefixJson) {
jsonGenerator.writeRaw("{} && ");
}
objectMapper.writeValue(jsonGenerator, returnValue);
out.flush();
out.close();
return null;
} catch (JsonProcessingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
return UNRESOLVED;
}
}
The only custom class used above is my annotation class @Json which includes one parameter called mixins. Here's how I implement this on the Controller side.
@Controller
public class Controller {
@Json({ @JsonMixin(target=MyTargetObject.class, mixin=MyTargetMixin.class) })
@RequestMapping(value="/my-rest/{id}/my-obj", method=RequestMethod.GET)
public @ResponseBody List<MyTargetObject> getListOfFoo(@PathVariable("id") Integer id) {
return MyServiceImpl.getInstance().getBarObj(id).getFoos();
}
}
That is some pretty awesome simplicity. The ModelAndViewResolver will automatically convert the return object to JSON and apply the annotated mix-ins as well.
The one "down side" (if you call it that) to this is having to revert back to the Spring 2.5 way of configuring this since the new 3.0 tag doesn't allow configuring the ModelAndViewResolver directly. Maybe they just overlooked this?
My Old Config (using Spring 3.1 style)
<mvc:annotation-driven />
My New Config (using Spring 2.5 style)
<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
<property name="customModelAndViewResolvers">
<list>
<bean class="my.package.mvc.JsonModelAndViewResolver" />
</list>
</property>
</bean>
^^ 3.0+ doesn't have a way to wire-in the custom ModelAndViewResolver. Hence, the switch back to the old style.
Here's the custom annotations:
Json
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Json {
/**
* A list of Jackson Mixins.
* <p>
* {@link http://wiki.fasterxml.com/JacksonMixInAnnotations}
*/
JsonMixin[] mixins() default {};
}
JsonMixin
public @interface JsonMixin {
public Class<? extends Serializable> target();
public Class<?> mixin();
}
