[BUG] [JAVA/KOTLIN] [SPRING] A reactive controller that returns a JSON array of strings does not generate an object serializable by Jackson

[TMRGZ]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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 generating a reactive controller that should return a JSON array of strings should generate a method that returns Mono<ResponseEntity<List> or Mono<ResponseEntity<Set> depending on the uniqueItems flag instead of Flux.

Related Spring documentation: https://docs.spring.io/spring-framework/reference/web/webflux/reactive-spring.html#webflux-codecs-jackson

Related Stackoverflow question: https://stackoverflow.com/questions/48421597/returning-fluxstring-from-spring-webflux-returns-one-string-instead-of-array-o

openapi-generator version

7.7.0

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: OpenAPI Petstore
  description: "sample to get all user id as string list and string set"
  version: 1.0.0
tags: []
paths:
  /users/id?type=set:
    get:
      operationId: getUserIdSet
      tags:
        - users
      responses:
        '200':
          description: response
          content:
            application/json:
              schema:
                type: array
                "uniqueItems": true
                "items":
                  "type": "string"

  /users/id?type=list:
    get:
      operationId: getUserIdList
      tags:
        - users
      responses:
        '200':
          description: response
          content:
            application/json:
              schema:
                type: array
                "uniqueItems": false
                "items":
                  "type": "string"

Generation Details

Maven settings used:

<configuration>
    <inputSpec>${project.basedir}/api/api.yaml</inputSpec>
    <generatorName>spring</generatorName>
    <generateApis>true</generateApis>
    <generateModels>true</generateModels>
    <!-- configuration -->
    <configOptions>
       <interfaceOnly>true</interfaceOnly>
       <sourceFolder>/src/main/java</sourceFolder>
       <useSpringBoot3>true</useSpringBoot3>
       <reactive>true</reactive>
     </configOptions>
 </configuration>

Steps to reproduce

1. Set up project
2. mvn clean compile

Related issues/PRs

Related but affecting the Java client
#16326

Suggest a fix

In case there there is an endpoint with application/json content type, create an exception to generate a collected collection of strings, the Kotlin Spring generator is affected too

[jorgerod]

Any news? Is there a workaround?