Quick question regarding which HttpMessageConverter is being used by default when using the `org.spr...

# spring

[Tim Schraepen]

Quick question regarding which HttpMessageConverter is being used by default when using the org.springframework.web.servlet.function.RouterFunctionDsl?
Because it doesn't seem to be the default configured objectmapper.

I just ran into a very annoying problem while livecoding.
I was getting json responses where a LocalDateTime was being converted into a [2024,6,4,....] format instead of a "2024-06-04T...." format, which is supposedly the default date-format of spring's configured Jackson ObjectMapper.

I ended up injecting the default ObjectMapper and doing conversion myself:

ServerResponse.ok()
    .contentType(MediaType.APPLICATION_JSON)
    .body(foundQuotes.toJson())

What am I missing?

[Tim Schraepen]

Code: https://github.com/kunlabora/kunlaquota-tim/blob/main/src/main/kotlin/be/kunlabora/crafters/kunlaquota/rest/http.kt

[Tim Schraepen]

Relevant part of the livestream: https://www.twitch.tv/videos/2163617916?t=01h13m57s

[kqr]

when you debug the instance of object mapper used, does it have features enabled/disabled as you expect/as is behaving?

[Tim Schraepen]

The workaround I have right now is to use the objectmapper -that Spring provides- directly in my route and that one is indeed configured according to the defaults I expect.

[Tim Schraepen]

But to directly answer your question, I don’t know which objectmapper, or rather which messageconverter, is used.

I also don’t exactly know how to find that information at runtime. There’s a list of messageconverters that belong to a context on a ServerResponse. But it’s difficult to pinpoint which one gets used at runtime when the http response is returned.

All I can verify is that it’s not the default objectmapper that Spring configures.

[kqr]

ah I misunderstood that code is already having workaround

[Tim Schraepen]

😅

[kqr]

I would set breakpoint in AbstractJackson2HttpMessageConverter#writeInternal to see what's going on

[Tim Schraepen]

It's a different objectMapper instance for sure. The object id's are different.
Any idea on identifying where it's coming from?

[Tim Schraepen]

It's the defaultObjectMapper of the AbstractJackson2HttpMessageConverter.
You'd think it's the same one as the

@Primary
@Bean
fun objectMapper() = jacksonObjectMapper()

[David Kubecka]

Did you manage to solve the issue? It happened to me as well and same as you I'm totally clueless as to which object mapper is used in the request serialization...

[Tim Schraepen]

The way I solved it was by manually injecting the ObjectMapper that I expected, without having to depend on Spring's default configuration.

[David Kubecka]

Ok, so you didn't find the root cause? Because this to me seems as a bug. In my mental model of Spring Boot app the same autoconfigured object mapper should be used everywhere. Or am I mistaken here?

[David Kubecka]

Also, what exactly was your context? Did you have problems with serialization of responses coming from your app? Because mine problem is with serialization of requests to 3rd party REST APIs.

[David Kubecka]

In the case of request body serialization I don't even know how/where to inject the working object mapper...

[Tim Schraepen]

I'll copy paste my original question:

I just ran into a very annoying problem while livecoding.

I was getting json responses where a LocalDateTime was being converted into a [2024,6,4,....] format instead of a "2024-06-04T...." format, which is supposedly the default date-format of spring's configured Jackson ObjectMapper.

[Tim Schraepen]

So it was indeed on the response, not the request.
I think you're correct that it'll likely fail if my api would accept json requests that contain differently formatted time fields

[Tim Schraepen]

It also feels like a bug to me.

[kqr]

Imho you have to configure custom MessageConverter

[kqr]

https://www.baeldung.com/spring-boot-customize-jackson-objectmapper

[David Kubecka]

The problem is that the objectMapper is already configured correctly and works, i.e. the output of objectMapper.writeValueAsString(request.body) has the dates formatted as expected. It's somewhere deep inside the request processing (before it is sent over the wire) that a misconfigured objectMapper is used.

[kqr]

issue is imho that messageConverter is not using "global" objectMapper

[kqr]

https://github.com/spring-projects/spring-boot/issues/12289

[David Kubecka]

I'm not using @EnableWebMvc , at least not directly. Will keep digging.

[Tim Schraepen]

I was. That indeed fixed the issue.
Thank you so much @kqr 🙏