Spring Boot register custom jackson (polygon) deserializer after Spring Boot upgrade 2.4->2.5

Question

TLDR; How can I tell spring to use my custom deserializer? (Yes, I checked but it's fubar)

I have a PostMapping equipped with a Polygon as RequestBody param; It takes a array of arrays (containing points) and should convert them to a org.elasticsearch.geometry.Polygon

@PostMapping(value = "/search", consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<List<SearchDTO>> findSpatialResults(@RequestBody Polygon polygon) {...}

As this need a custom deserializer, this is it;

public class PolygonDeserializer extends StdDeserializer<Polygon> {

    public PolygonDeserializer() {
        super(Polygon.class);
    }

    @Override
    public Polygon deserialize(JsonParser jp, DeserializationContext context)
            throws IOException {
        ObjectCodec oc = jp.getCodec();
        JsonNode node = oc.readTree(jp);
      ...
    }
}

Which is registered in a @Configuration annotated SpringConfig class;

@Configuration
public class SpringConfig {

    @Bean
    public Module polygonDeserializer() {
        SimpleModule module = new SimpleModule();
        module.addDeserializer(Polygon.class, new PolygonDeserializer());
        return module;
    }
}

Before updating Spring this worked, now I get a JSON parse error: Cannot deserialize instance of `org.elasticsearch.geometry.Polygon` out of START_ARRAY token and can't figure out why.

Answer 1

I was using two @configuration annotated classes.

Fixed by adding the first config (WebConfig.class) into SpringConfig.class and registering it as a Bean;

@Configuration
public class SpringConfig {

    @Bean
    public ModelMapper modelMapper() {
        return new ModelMapper();
    }

    @Bean
    public WebConfig webConfig() {
        return new WebConfig();
    }

    @Bean
    public Module polygonDeserializer() {
        SimpleModule module = new SimpleModule();
        module.addDeserializer(Polygon.class, new PolygonDeserializer());
        return module;
    }
}

Second config before change;

@EnableWebMvc
@Configuration //<---- **Issue**
public class WebConfig implements WebMvcConfigurer {

    ...

    @Override
    public void addCorsMappings(CorsRegistry registry) {
    ...
    }
}

Spring calls only one of the two config classes and does not register the custom deserializer.