Provide intelligent defaults for web flux types Mono and Flux

[dilipkrish]

Hi @dilipkrish, just wanted to check before opening an issue.

In Webflux projects, the generated responses and definitions don't seem to be correct when returning a Mono or Flux.

Simple DTO:

public class HelloDto {
    private final String message;
    ...

Controller

        @GetMapping("/hello")
        public Mono<HelloDto> hello() {
            return Mono.fromSupplier(() -> new HelloDto("Hello SpringFox!"));
        }
        
        @GetMapping("/hellos")
        public Flux<HelloDto> hellos() {
            return Flux.just(new HelloDto("Hello SpringFox!"));
        }

Generated definitions:

    "paths": {
        "/functional-hello/hello": {
            "get": {
                "tags": [
                    "functional-hello-world-controller"
                ],
                "summary": "hello",
                "operationId": "helloUsingGET",
                "produces": [
                    "*/*"
                ],
                "responses": {
                    "200": {
                        "description": "Ok",
                        "schema": {
                            "$ref": "#/definitions/Mono«HelloDto»"
                        }
                    },
                    "401": {
                        "description": "Unauthorized"
                    },
                    "403": {
                        "description": "Forbidden"
                    },
                    "404": {
                        "description": "Not Found"
                    }
                }
            }
        },
        "/functional-hello/hellos": {
            "get": {
                "tags": [
                    "functional-hello-world-controller"
                ],
                "summary": "hellos",
                "operationId": "hellosUsingGET",
                "produces": [
                    "*/*"
                ],
                "responses": {
                    "200": {
                        "description": "Ok",
                        "schema": {
                            "$ref": "#/definitions/Flux«HelloDto»"
                        }
                    },
                    "401": {
                        "description": "Unauthorized"
                    },
                    "403": {
                        "description": "Forbidden"
                    },
                    "404": {
                        "description": "Not Found"
                    }
                }
            }
        }
    },
    "definitions": {
        "Flux«HelloDto»": {
            "type": "object",
            "properties": {
                "prefetch": {
                    "type": "integer",
                    "format": "int32"
                }
            },
            "title": "Flux«HelloDto»"
        },
        "HelloDto": {
            "type": "object",
            "properties": {
                "message": {
                    "type": "string"
                }
            },
            "title": "HelloDto"
        },
        "Mono«HelloDto»": {
            "type": "object",
            "title": "Mono«HelloDto»"
        }
    }
}

As you can see /functional-hello/hello has a response with this definition #/definitions/Mono«HelloDto» which is

        "Mono«HelloDto»": {
            "type": "object",
            "title": "Mono«HelloDto»"
        }

Shouldn't it just point at #/definitions/HelloDto which has the actual definition?

        "HelloDto": {
            "type": "object",
            "properties": {
                "message": {
                    "type": "string"
                }
            },
            "title": "HelloDto"
        },

The same happens for Flux. I guess it shoud be a response with and array of #/definitions/HelloDto

What do you think?

BTW I tried explicitly using @ApiResponse annotations and didn't make any change:

@ApiResponses(@ApiResponse(code = 200, message = "Ok", response = HelloDto.class))
...
@ApiResponses(@ApiResponse(code = 200, message = "Ok", response = HelloDto.class, responseContainer = "List"))
...

Originally posted by @svpr3m0 in #3070 (comment)