[BUG][Java][RestClient][jackson3] restclient.messageConverters unset for ApiClient with default construction

[chumbalum]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

• when constructing an ApiClient with the default constructor, the internal generated RestClient will not have any messageConverters set, resulting in errors like

Could not extract response: no suitable HttpMessageConverter found for response type [class ag.xyz.model.SomethingDto] and content type [application/json]

• with the pull request to support jackson3, logic for adding JacksonJsonHttpMessageConverter to the rest client was added (which will be used, if useJackson3 is true
  • https://github.com/OpenAPITools/openapi-generator/pull/23023/changes#top (see ApiClient.mustache)
• to achieve it, the method .withJsonConverter was used
  • https://github.com/spring-projects/spring-framework/blob/3be51b1c77617e2e199958ca4fc96fc82b4bd50b/spring-web/src/main/java/org/springframework/http/converter/DefaultHttpMessageConverters.java#L411
• the build method DefaultHttpMessageConverters will only pick up the jsonConverter as part of getCoreConverters(), if registerDefaults is set (by .registerDefaults())
  • https://github.com/spring-projects/spring-framework/blob/3be51b1c77617e2e199958ca4fc96fc82b4bd50b/spring-web/src/main/java/org/springframework/http/converter/DefaultHttpMessageConverters.java#L482
  • the build method is called via initMessageConverters in DefaultRestClientBuilder
    • https://github.com/spring-projects/spring-framework/blob/3be51b1c77617e2e199958ca4fc96fc82b4bd50b/spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java#L508

openapi-generator version

• openapi-generator-maven-plugin 7.21.0
• spring framework 7.0.6

additional params used

<useSpringBoot4>true</useSpringBoot4>
<useJackson3>true</useJackson3>
<library>restclient</library>
<openApiNullable>false</openApiNullable>
<useJakartaEe>true</useJakartaEe>
<generateBuilders>true</generateBuilders>
<useSingleRequestParameter>static</useSingleRequestParameter>
<useAbstractionForFiles>true</useAbstractionForFiles>

Steps to reproduce

• create ApiClient with default constructor
• apiClient.restClient.messageConverters will be empty

this.apiClient = new ApiClient();

• create ApiClient with construction like in mustache template
• apiClient.restClient.messageConverters will be empty

this.apiClient = new ApiClient(RestClient.builder()
		.configureMessageConverters(c -> c
				.withJsonConverter(new JacksonJsonHttpMessageConverter())
		)
		.build()
);

• create ApiClient with construction like in mustache template, but use registerDefaults
• apiClient.restClient.messageConverters will have entries (5), including the JacksonJsonHttpMessageConverter

this.apiClient = new ApiClient(RestClient.builder()
		.configureMessageConverters(c -> c
				.registerDefaults()
				.withJsonConverter(new JacksonJsonHttpMessageConverter())
		)
		.build()
);

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/pull/23023/changes#top (see ApiClient.mustache)

Suggest a fix

• adding registerDefaults() beforehand withJsonConverter(...) will lead to existing messageConverters, nevertheless I'm not too deep into it, to see the full consequences

[jpfinne]

@chumbalum It seems to be a bug in Spring-web 7 (https://github.com/spring-projects/spring-framework/blob/4709f684468ebc12a8603b4ec452c306a5809947/spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java#L500). RegisterDefaults() is not called when convertersConfigurer is <> null.
RestClient.builder().build creates 6 converters, but when you want to configure one, there is no converter at all!

I've stumbled on this issue. registerDefaults() needs to be called.

[stil4m]

This seems to get fixed in Spring 7.0.7:
spring-projects/spring-framework#36579 (see Milestone)/

Might be worth waiting for that.
Downgrading from 7.21.0 to 7.20.0 seems to work for now.

[chumbalum]

This seems to get fixed in Spring 7.0.7: spring-projects/spring-framework#36579 (see Milestone)/

Might be worth waiting for that. Downgrading from 7.21.0 to 7.20.0 seems to work for now.

Good catch. Seems to exactly match this topic. Since, as noted in my report, there is at least a workaround which can be used in the meantime, i'll close this issue for now. So hopefully it will get fixed on the spring side anytime soon.

Thanks for the input guys.