importMappings does not work in REF yaml file.

Description

feature does mot works in referenced documents.

  <importMappings>
        <importMapping>JavaClass=com.timosh.user.MyClassToReplace</importMapping>
         <importMapping>ExternalClass=com.timosh.user.MyClassToReplace</importMapping>
         <importMapping>json_myclass=com.timosh.user.MyClassToReplace</importMapping>
</importMappings>

In User.java the  Pet has 'Object' type
 @JsonProperty("pet")
  private Object pet = null;

In Pet.java also Object type
  @JsonProperty("javaSimpleClass")
  private Object javaSimpleClass = null;

openapi-generator version

Version 5.1.0

OpenAPI declaration file content or url

user.yml

openapi: 3.0.2
info:
  title: Test OpenAPI specification
  description: "Tutorials on OpenApi"
  version: 0.0.1-SNAPSHOT

tags:
  - name: user
    description: Operations about user
    externalDocs:
      description: Find out more about our store
      url: http://swagger.io

servers:
  - url: https://api.phrase.com/v2

paths:
  /user/{username}:
    get:
      tags:
        - user
      summary: Get user by user name
      parameters:
        - name: username
          in: path
          description: 'The name that needs to be fetched. Use user1 for testing. '
          required: true
          schema:
            type: string
      responses:
        200:
          description: successful operation
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'
        404:
          description: User not found
          content: { }

components:
  schemas:
    Message:
      type: object
      required:
        - code
        - text
      properties:
        code:
          type: integer
        text:
          type: string
          pattern: '^\d{2}-\d{2}$'
    Element:
      type: object
      properties:
        text:
          type: string
          pattern: '^\d{2}-\d{2}$'
    User:
      type: object
      properties:
        id:
          type: integer
          format: int64
        username:
          type: string
          minLength: 4
          maxLength: 100
        firstName:
          type: string
        pet:
          $ref: './pet.yml#/components/schemas/Pet'
        javaClass:
          $ref: "#/components/schemas/JavaClass"
        javaSimpleClass:
            $ref: "#/components/schemas/json_myclass"
        my_boolean:
          type: boolean
          x-codegen-body-parameter-name: boolean_post_body

pet.yml

components:
  schemas:
    Pet:
      type: object
      required:
        - petName
      properties:
        id:
          type: integer
          format: int64
        javaSimpleClass:
          $ref: "#/components/schemas/JavaClass"
        petName:
          type: string
          nullable: false
          minLength: 4
          maxLength: 100

Command line used for generation

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>my.timosh.openapi.demo</groupId>
    <version>0.1.0</version>
    <artifactId>specification-demo</artifactId>

    <properties>

        <java.version>8</java.version>
        <swagger-annotations-version>1.5.22</swagger-annotations-version>
        <jackson-version>2.10.2</jackson-version>
        <springfox-version>3.0.0</springfox-version>
        <spring-boot-starter-test-version>2.1.1.RELEASE</spring-boot-starter-test-version>
        <spring-boot-starter-web-version>2.1.0.RELEASE</spring-boot-starter-web-version>
        <jackson-databind-nullable>0.2.1</jackson-databind-nullable>
        <junit-version>5.7.1</junit-version>

    </properties>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>${spring-boot-starter-web-version}</version>
        </dependency>

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>${springfox-version}</version>
        </dependency>

        <dependency>
            <groupId>org.openapitools</groupId>
            <artifactId>jackson-databind-nullable</artifactId>
            <version>${jackson-databind-nullable}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.11</version>
        </dependency>

        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>${junit-version}</version>
            <scope>test</scope>
        </dependency>


        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>${junit-version}</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>5.1.0</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/src/main/openapi/openapi.yml</inputSpec>
                            <generatorName>spring</generatorName>

                            <skipValidateSpec>true</skipValidateSpec>

                            <supportingFilesToGenerate>AppUtils.java</supportingFilesToGenerate>
                            <modelPackage>my.timosh.demo.model</modelPackage>
                            <generateApis>false</generateApis>
                            <generateModelTests>false</generateModelTests>

                            <importMappings>
                                <importMapping>JavaClass=com.timosh.user.MyClassToReplace</importMapping>
                                <importMapping>ExternalClass=com.timosh.user.MyClassToReplace</importMapping>
                                <importMapping>json_myclass=com.timosh.user.MyClassToReplace</importMapping>
                            </importMappings>

                            <configOptions>
                                <java8>true</java8>
                                <delegatePattern>false</delegatePattern>
                                <useBeanValidation>true</useBeanValidation>
                                <performBeanValidation>true</performBeanValidation>
                                <serializableModel>false</serializableModel>
                            </configOptions>
                        </configuration>
                    </execution>
                </executions>

            </plugin>


            <plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.2</version>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <proc>none</proc>
                </configuration>
            </plugin>
        </plugins>
    </build>


</project>

Steps to reproduce

mvn clean compile

Suggest a fix/enhancement

Start with the user.yml and pet.yml OpenAPI documents and the Spring generator configuration containing importMappings. Run mvn clean compile to reproduce the generated Java models, then compare the referenced Pet and JavaClass fields with the requested mappings for JavaClass, ExternalClass, and json_myclass. Done means those mappings are applied in referenced documents instead of producing Object fields.