[BUG] [jaxrs-spec] [quarkus] Code Generation creates invalid structure for multipart/form-data

Bug Report Checklist

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

Description

Hello everyone,

I'm currently trying to get my file upload service running with Quarkus, but I ran into an issue with the generated code from the OpenAPI Generator for the jaxrs-spec.

The generator produces invalid code for multipart/form-data requests. When I start my Quarkus application, I receive the following error:

Caused by: java.lang.RuntimeException: RESTEASY003875: Unable to find a constructor that takes a String param or a valueOf() or fromString() method for jakarta.ws.rs.FormParam("documentMetaData") on public abstract jakarta.ws.rs.core.Response com.example.api.DocumentsApi.updateDocumentById(java.lang.String,com.example.api.model.DocumentDTO,java.io.InputStream,java.lang.String) for basetype: com.example.api.model.DocumentDTO
	at org.jboss.resteasy.core.StringParameterInjector.initialize(StringParameterInjector.java:579)
	at org.jboss.resteasy.core.StringParameterInjector.<init>(StringParameterInjector.java:515)

The OpenAPI Generator creates the following interface:

     */
    @POST
    @Consumes({ "multipart/form-data" })
    @Produces({ "application/json" })
    Response createDocument(@FormParam(value = "documentMetaData")  DocumentDTO documentMetaData, @FormParam(value = "file") InputStream _fileInputStream,@FormParam(value = "filename")  String filename);

    @PUT
    @Path("/{documentId}")
    @Consumes({ "multipart/form-data" })
    @Produces({ "application/json" })
    Response updateDocumentById(@PathParam("documentId") String documentId,@FormParam(value = "documentMetaData")  DocumentDTO documentMetaData, @FormParam(value = "file") InputStream _fileInputStream,@FormParam(value = "filename")  String filename);

However, this approach doesn't work with Quarkus. When handling multipart/form-data, Quarkus expects a single @MultipartForm-annotated class that wraps all parts of the request. Inside that class, fields are annotated with @FormParam and @PartType, as described in the official guide: https://quarkus.io/guides/resteasy-client-multipart#setting-up-the-model

The current generator ignores this requirement and produces a flat method signature instead of using a proper wrapper class, which causes the runtime error shown above.

I've found a related issue here that seems to point in the same direction:
https://github.com/OpenAPITools/openapi-generator/issues/7994

To sum it up:
Does anyone know how to solve this issue? Has anyone faced a similar problem or found a workaround (e.g., custom template, generator option, or plugin)?
Any help would be greatly appreciated!

Thanks in advance!

openapi-generator version

7.14.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Document Service API
  version: 1.0.0

paths:
  /documents:
    post:
      summary: Create a new document
      description: Uploads a new document and returns the created document.
      operationId: createDocument
      tags:
        - Documents
      requestBody:
        $ref: '#/components/requestBodies/CreateDocumentRequestBody'
      responses:
        '201':
          $ref: '#/components/responses/DocumentResponse'
        '400':
          $ref: '#/components/responses/BadRequestErrorResponse'
        '401':
          $ref: '#/components/responses/UnauthorizedErrorResponse'
        '403':
          $ref: '#/components/responses/ForbiddenErrorResponse'
        '422':
          $ref: '#/components/responses/UnprocessableEntityErrorResponse'
        5XX:
          $ref: '#/components/responses/ServerErrorResponse'

  /documents/{documentId}:
    put:
      summary: Update an existing document
      description: Stores a new document and returns the updated document.
      operationId: updateDocumentById
      tags:
        - Documents
      parameters:
        - name: documentId
          in: path
          required: true
          schema:
            type: string
          description: The ID of the document to update
      requestBody:
        $ref: '#/components/requestBodies/CreateDocumentRequestBody'
      responses:
        '200':
          $ref: '#/components/responses/DocumentResponse'
        '400':
          $ref: '#/components/responses/BadRequestErrorResponse'
        '401':
          $ref: '#/components/responses/UnauthorizedErrorResponse'
        '403':
          $ref: '#/components/responses/ForbiddenErrorResponse'
        '404':
          $ref: '#/components/responses/NotFoundErrorResponse'
        '422':
          $ref: '#/components/responses/UnprocessableEntityErrorResponse'
        5XX:
          $ref: '#/components/responses/ServerErrorResponse'

components:
  requestBodies:
    CreateDocumentRequestBody:
      required: true
      content:
        multipart/form-data:
          schema:
            $ref: '#/components/schemas/CreateDocumentRequest'


  schemas:
    DocumentDTO:
      type: object
      properties:
        title:
          type: string
        type:
          type: string
        createdAt:
          type: string
          format: date-time
        createdBy:
          type: string
      required:
        - title
        - type

    CreateDocumentRequest:
      type: object
      additionalProperties: false
      properties:
        documentMetaData:
          $ref: '#/components/schemas/DocumentDTO'
        file:
          type: string
          format: binary
          description: The binary file content of the document
          maxLength: 9999999999999
        filename:
          type: string
          description: The name of the file
          maxLength: 255
          pattern: ^.*$
          example: Trial.pdf
      required:
        - documentMetaData
        - file
        - filename

  responses:
    DocumentResponse:
      description: Successful response containing document details
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/DocumentDTO'

    BadRequestErrorResponse:
      description: The request is invalid

    UnauthorizedErrorResponse:
      description: Authentication is required

    ForbiddenErrorResponse:
      description: Access is forbidden

    NotFoundErrorResponse:
      description: Document not found

    UnprocessableEntityErrorResponse:
      description: Validation or semantic error

    ServerErrorResponse:
      description: Internal server error

Generation Details

   <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>7.14.0</version>
                <executions>
                    <execution>
                        <id>generate-document</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/src/main/resources/openapi.yaml</inputSpec>
                            <generatorName>jaxrs-spec</generatorName>
                            <output>${project.build.directory}/generated-sources/openapi</output>
                            <apiPackage>com.example.api</apiPackage>
                            <invokerPackage>com.example.api</invokerPackage>
                            <modelPackage>com.example.api.model</modelPackage>
                            <globalProperties>
                                <skipFormModel>false</skipFormModel>
                            </globalProperties>
                            <configOptions>
                                <useOneOfInterfaces>true</useOneOfInterfaces>
                                <useJakartaEe>true</useJakartaEe>
                                <library>quarkus</library>
                                <dateLibrary>java8</dateLibrary>
                                <useJakartaEe>true</useJakartaEe>
                                <useSwaggerAnnotations>false</useSwaggerAnnotations>
                                <openApiNullable>false</openApiNullable>
                                <interfaceOnly>true</interfaceOnly>
                                <generateRootResource>false</generateRootResource>
                                <returnResponse>true</returnResponse>
                            </configOptions>
                            <typeMappings>
                                <typeMapping>DateTime=LocalDateTime</typeMapping>
                            </typeMappings>
                            <importMappings>
                                <importMapping>LocalDateTime=java.time.LocalDateTime</importMapping>
                            </importMappings>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

Steps to reproduce

Generate java code from the openapi.yml above using the jaxrs-spec generator and the quarkus library

FYI these are the other dependency from my pom.xml:

    <properties>
        <compiler-plugin.version>3.14.0</compiler-plugin.version>
        <maven.compiler.release>21</maven.compiler.release>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <quarkus.platform.artifact-id>quarkus-bom</quarkus.platform.artifact-id>
        <quarkus.platform.group-id>io.quarkus.platform</quarkus.platform.group-id>
        <quarkus.platform.version>3.24.5</quarkus.platform.version>
        <skipITs>true</skipITs>
        <surefire-plugin.version>3.5.3</surefire-plugin.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>${quarkus.platform.group-id}</groupId>
                <artifactId>${quarkus.platform.artifact-id}</artifactId>
                <version>${quarkus.platform.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-smallrye-openapi</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-resteasy-multipart</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-resteasy</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-resteasy-client-jackson</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-resteasy-jackson</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-arc</artifactId>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-junit5</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>io.rest-assured</groupId>
            <artifactId>rest-assured</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/7994

Start by reproducing the generated interface with the provided OpenAPI declaration, the jaxrs-spec generator, and the Quarkus library configuration. Compare the flat multipart/form-data parameters with Quarkus's documented @MultipartForm model; done should be generated code that starts successfully and handles the documented multipart request without the RESTEasy constructor error.