[REQ] Handle list of String special case in webclient generator

[dlicois]

Is your feature request related to a problem? Please describe.

When describing an operation that returns an array of string, the openapi-generator for java-webclient generates an api returning a Flux<String>.

However Spring's Webclient handles serialization of JSON array of strings in a special way : spring-projects/spring-framework#22662

This means expecting a Flux<String> when a server return an array of String is a mistake.

Please see sample Gradle project https://github.com/dlicois/webclient-liststring, it contains a test class (WebClientListStringTest.java) to better explain the behaviour.
The openapi.yaml describes an operation returning an array of string, openapi-generator generates a DefaultApi.java class returning a Flux<String>.
When the webclient receive the answer ["one","two", "three"], it publishes a single String of value ["one","two", "three"].
I would have expected three Strings.

This makes the generated api unusable for this case, requiring to parse the response a second time to handle it.

Describe the solution you'd like

Recommended solution by Spring developers (see spring-projects/spring-framework#22662 and https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-codecs-jackson) is to use a Mono<List> for string arrays.

This would mean making a special case for operations described as arrays of string to generate a Mono<List> instead of Flux.

[bossqone]

Same issue with java spring generator when @RequestBody is used with Flux<String> to parse json request ["a", "b", "c"].

[garzy]

I'm having the same issue ¿won't be fixed yet in 2022? this issue was opened in 2020, please fix them

I'm generating WebClient code with the 5.4.0 version of open API-generator cli.

[yasammez]

I can confirm the problem still exists in version 6.2.1 of openapi-generator. For now, the only option seems to be to wrap the array in a useless JSON object (that is, if you control the API as well as the implementation).

[giftkugel]

Facing the same issue!

Generator is creating the interface with Mono<ResponseEntity<Flux<String>>>

Used version of openAPI Generator

I am using 6.2.0, because 6.2.1 leads to a OutOfMemoryError 🤷

                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>6.2.0</version>
...
                            <generatorName>spring</generatorName>
                            <library>spring-boot</library>

Response defined in openAPI YAML

      responses:
        '200':
          content:
            application/json:
              schema:
                type: array
                items:
                  type: string

Generated Controller/Interface

        default Mono<ResponseEntity<Flux<String>>> foo(...,ServerWebExchange exchange)

Expected JSON Response

["1", "2", "3", "4"]

Current JSON Response

1234