[BUG][JAVA] Different media types per HTTP status code cause misleading generation of @ApiResponse

Description

I was trying to define an RFC 9457 compliant Problem object that uses the "application/problem+json" media type. In this scenario, all 4xx or 5xx HTTP status codes would lead to a predefined Object as "application/problem+json" while 2xx would return the actual payload object as "application/json".

The example below reproduces the issue with a simple GET /test that yields 200 and 404.

The generated code suggests, that both HTTP status codes would yield both "application/json" and "application/problem+json".

openapi-generator version

This has been reproduced with 7.4.0 as well as with the current HEAD (f357be4)

OpenAPI declaration file content or url

This is simplest specification to reproduce the issue (referred to as spec.yaml)

  openapi: 3.1.0
  info:
    title: Demo
    version: 1.0.0
  paths:
    /test:
      get:
        responses:
          '200':
            description: Success
            content:
              application/json:
                schema:
                  type: string
          '400':
            description: Error
            content:
              application/problem+json:
                schema:
                  type: string

Generation Details

• Check out and build project as described here (https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-to-test-with-the-latest-master-of-openapi-generator)
• java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g spring -i spec.yaml -o generated

Steps to reproduce

• Generate code as described above
• generated\src\main\java\org\openapitools\api\TestApi.java

Generated code:

    // ...
    @Operation(
        operationId = "testGet",
        responses = {
            @ApiResponse(responseCode = "200", description = "Success", content = {
                @Content(mediaType = "application/json", schema = @Schema(implementation = String.class)),
                @Content(mediaType = "application/problem+json", schema = @Schema(implementation = String.class))
            }),
            @ApiResponse(responseCode = "400", description = "Some error", content = {
                @Content(mediaType = "application/json", schema = @Schema(implementation = String.class)),
                @Content(mediaType = "application/problem+json", schema = @Schema(implementation = String.class))
            })
        }
    )
    // ...

Expected code:

    // ...
    @Operation(
        operationId = "testGet",
        responses = {
            @ApiResponse(responseCode = "200", description = "Success", content = {
                @Content(mediaType = "application/json", schema = @Schema(implementation = String.class)),
            }),
            @ApiResponse(responseCode = "400", description = "Some error", content = {
                @Content(mediaType = "application/problem+json", schema = @Schema(implementation = String.class))
            })
        }
    )
    // ...

Related issues/PRs

Possible, I didn't find any

Suggest a fix

This is more of an observation than a fix: JavaSpring/api.mustache uses the produces list to generate @Content annotations with @ApiResonse. This list (templateData > operations.0.produces) contains all media types within the operation.

Debugging into org.openapitools.codegen.DefaultGenerator#processTemplateToFile suggests that (templateData > operations.0.responses.[].content) contains the actual media type for this response.

Start with JavaSpring/api.mustache and inspect how templateData > operations.0.responses[].content is populated in DefaultGenerator#processTemplateToFile. Reproduce the issue with spec.yaml and inspect generated/src/main/java/org/openapitools/api/TestApi.java. Done means each @ApiResponse contains only the media type defined for its HTTP status code.