[Java spring] Failed to generate multi-part request body

Hey guys!

[Java spring] When using multipart/form-data in requestBody, codegen fails to generate corresponding parameter in API.

And using application/json works fine.

Swagger-codegen version

3.0.34

Yaml

Using multipart/form-data as content type:

  /insight/v1/attachments:download:
    post:
      tags:
        - CustomerProfileAttachmentRestService
      description: batch download files
      summary: download files
      operationId: downloadCustomerProfileDocuments
      requestBody:
        description: file multi parts
        required: true
        content:
          multipart/form-data:
            schema:
              type: array
              items:
                type: string
                minLength: 1
      responses:
        200:
          description: Successful response
          content:
            application/json:
              schema:
                type: object # just for testing, not a real response 

And it failed to generate param.

After debuging, what I found is that in AbstractJavaCodegen , method postProcessOperations, the corresponding operation in its return object "objs" has wrong content, which its contentType is null. And eventually cause failure of generating such param.

And in contract, yaml like below, which just change the content media type to application/json, are manage to generate properly.

  /insight/v1/attachments:download:
    post:
      tags:
        - CustomerProfileAttachmentRestService
      description: batch download files
      summary: download files
      operationId: downloadCustomerProfileDocuments
      requestBody:
        description: file multi parts
        required: true
        content:
          application/json:
            schema:
              type: array
              items:
                type: string
                minLength: 1
      responses:
        200:
          description: Successful response
          content:
            application/json:
              schema:
                type: object # just for testing, not a real response 

Debugging shows that the content of CodegenOperation is right, which its contentType is application/json and it contains a parameter. Then it generate param properly.

Suggest a fix/enhancement

At least, developers are manageed to get the content below such media type multipart/form-data, instead of nothing at all in content, and we cannot find these content anywhere else.

And I still cannot figure out why multipart/form-data is not supported, since its allowed by OpenApi 3.0.x.

Thanks!

Start with AbstractJavaCodegen.postProcessOperations and the supplied OpenAPI YAML, comparing the multipart/form-data and application/json cases. Inspect how the CodegenOperation contentType and parameters are populated. Done means the multipart request body produces the corresponding generated parameter instead of being omitted.