[BUG] [spring] Request Body is not parsed correctly when using oas3 option

Created by: WIStudent

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

I am trying to use the new oas3 annotations introduced in https://github.com/OpenAPITools/openapi-generator/pull/9775 using the 5.3.1-SNAPSHOT version and the <oas3>true</oas3> option. I ran into the issue that the request body is not getting parsed correctly, the fields of the LogEntry object are all null. Adding the @org.springframework.web.bind.annotation.RequestBody annotation to the generated code like this PR does fixes it.

The main goal of this issue is to raise awareness for this problem and the existing PR that fixes it.

openapi-generator version

5.3.1-SNAPSHOT

OpenAPI declaration file content or url

openapi: "3.0.2"
info:
  title: title
  description: description
  version: "1.0"

paths:
  "/app/log":
    summary: Add a new log entry
    post:
      tags:
        - log
      operationId: log
      requestBody:
        $ref: '#/components/requestBodies/LogBody'
      responses:
        '200':
          description: ok, the entry was NOT created because the level was too low
        '201':
          description: created
        '401':
          $ref: '#/components/responses/UnauthorizedError'

components:
  responses:
    UnauthorizedError:
      description: Access token is missing or invalid
  requestBodies:
    LogBody:
      required: true
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/LogEntry'
  schemas:
    LogEntry:
      type: object
      properties:
        level:
          type: string
          enum:
            - debug
            - info
            - warning
            - error
        message:
          type: string
      required:
        - level
        - message

Generation Details

I am using the maven plugin, here is the configuration:

<plugin>
    <groupId>org.openapitools</groupId>
    <artifactId>openapi-generator-maven-plugin</artifactId>
    <version>5.3.1-SNAPSHOT</version>
    <executions>
        <execution>
            <id>openapi-generator-server</id>
            <goals>
                <goal>generate</goal>
            </goals>
            <configuration>
                <inputSpec>openapi-spec.yaml</inputSpec>
                <generatorName>spring</generatorName>
                <apiPackage>com.example.openapi.api</apiPackage>
                <modelPackage>com.example.openapi.model</modelPackage>
                <supportingFilesToGenerate>
                    ApiUtil.java
                </supportingFilesToGenerate>
                <configOptions>
                    <delegatePattern>true</delegatePattern>
                    <dateLibrary>java8</dateLibrary>
                    <oas3>true</oas3>
                    <useSpringController>true</useSpringController>
                </configOptions>
            </configuration>
        </execution>
    </executions>
</plugin>

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/9775 https://github.com/OpenAPITools/openapi-generator/pull/10766

Suggest a fix

Merge https://github.com/OpenAPITools/openapi-generator/pull/10766