Java – Swagger UI not showing example value and model

I was generating Swagger API specification from Spring Boot REST controllers using Springfox.

I noticed an issue where the example value/model could not be shown for response.

As an investigation, I checked the JSON API doc at http://localhost:8080/v2/api-docs ,
and converted it to YMAL at https://editor.swagger.io/ , which it could not show the example value/model as well.
This seems to caused by the schema is not referring to the model object ("Car" here) correctly.

But from the API documentation of Swagger (https://docs.swagger.io/swagger-core/v1.5.0/apidocs/io/swagger/annotations/ApiResponse.html#response()), it says that the "response" attribute of the annotation @ApiResponse should correspond to the "schema" field of the specification.

By specifying response = "Object.class", shouldn't the Swagger UI populate the example value/model accordingly?

Welcome for any advice, and please kindly correct if I have any misconfigurations/misconceptions, thank you very much.

REST controller and the annotations:

@GetMapping(path = "/car")
@ApiOperation(value = "Get car by color.", response = Car.class)
@ApiParam(value = "Color of the car.", required = true)
@ApiResponses(value = { @ApiResponse(code = 200, message = "OK.", response = Car.class),
        @ApiResponse(code = 400, message = "Invalid color provided."),
        @ApiResponse(code = 404, message = "Car not found.") })
public ResponseEntity<Object> getCarByColor(@RequestParam String color) {
    return ResponseEntity.ok(testService.getCarByColor(color));
}

Model:

package com.example.demo.model;

import javax.validation.constraints.Max;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Pattern;

import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;

@ApiModel(value = "Car", description = "The model for car")
@Data
public class Car {
    @ApiModelProperty(notes = "Car ID.", example = "12345", required = false, position = 0)
    private Long id;

    @ApiModelProperty(notes = "Car name.", example = "Suzuki Swift 2020", required = true, position = 1)
    @NotNull
    @Max(value = 30, message = "Name can only have a maximum length of 30")
    private String name;

    @ApiModelProperty(notes = "Car color.", example = "blue", required = true, position = 2)
    @NotNull
    @Max(value = 30, message = "Color can only have a maximum length of 30")
    @Pattern(regexp = "^(blue|yellow)$", message = "Only blue or yellow color is allowed.")
    private String color;

    public Car(Long id, String name, String color) {
        this.id = id;
        this.name = name;
        this.color = color;
    }
}

Swagger UI:

Springfox dependency in pom.xml:

    <dependency>
        <groupId>io.springfox</groupId>
        <artifactId>springfox-boot-starter</artifactId>
        <version>3.0.0</version>
    </dependency>

<UPDATE (31 Jul 2020)>

Made the following changes to use OAS3.0 specification and annotations, but still have issue. It also gives an error in Swagger UI.

REST controller and the annotations:

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.responses.ApiResponse;

...
......

@GetMapping(path = "/car", produces = "application/json")
@Operation(summary = "Get car by color.", responses = {
        @ApiResponse(responseCode = "200", description = "OK.", content = {
                @Content(mediaType = "application/json", schema = @Schema(type = "object", implementation = Car.class)) }) })
public ResponseEntity<Object> getCarByColor(@RequestParam String color) {
    return ResponseEntity.ok(testService.getCarByColor(color));
}

Model:

package com.example.demo.model;

import javax.validation.constraints.Max;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Pattern;

import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import io.swagger.v3.oas.annotations.media.Schema;
import lombok.Data;

@ApiModel(value = "Car", description = "The model for car")
@Schema
@Data
public class Car {
    @ApiModelProperty(notes = "Car ID.", example = "12345", required = false, position = 0)
    private Long id;

    @ApiModelProperty(notes = "Car name.", example = "Suzuki Swift 2020", required = true, position = 1)
    @NotNull
    @Max(value = 30, message = "Name can only have a maximum length of 30")
    private String name;

    @ApiModelProperty(notes = "Car color.", example = "blue", required = true, position = 2)
    @NotNull
    @Max(value = 30, message = "Color can only have a maximum length of 30")
    @Pattern(regexp = "^(blue|yellow)$", message = "Only blue or yellow color is allowed.")
    private String color;

    public Car(Long id, String name, String color) {
        this.id = id;
        this.name = name;
        this.color = color;
    }
}

Swagger UI: