[BUG][Java][Spring] Models not generated correctly when identical names used from schemas

Description

When generating models using the spring or java generator, if the spec uses external references and there are name conflicts internally, it will not generate the models you would expect.

openapi-generator version

I am using the openapi-generator-maven-plugin version 7.18.0

OpenAPI declaration file content or url

The following is a minimum example:

openapi.yaml

openapi: 3.1.0
info:
  title: Example API
  version: "1.0.0"
  description: A small OpenAPI 3.1.0 document exposing two endpoints for managing items.
paths:
  /items:
    get:
      summary: List all items
      operationId: listItems
      responses:
        "200":
          description: The Item
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: string
                  item:
                    $ref: './test1.yaml#/components/schemas/Item'
  /items2:
    get:
      summary: List all items 2
      operationId: listItems2
      responses:
        "200":
          description: The Item
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: string
                  item:
                    $ref: './test2.yaml#/components/schemas/Item'

test1.yaml

openapi: 3.1.0
info:
  title: Test 1
  version: "1.0.0"
  description: Test 1
components:
  schemas:
    Item:
      title: Item
      type: object
      properties:
        weightUnitOfMeasure:
          $ref: '#/components/schemas/WeightUnitOfMeasure'
    WeightUnitOfMeasure:
      title: Weight Unit of Measure
      type: string
      description: A weight unit of measure
      enum:
        - Grams
        - Kilograms
        - MetricTons
        - Ounces
        - Pounds
        - Tons
      default: Pounds

test2.yaml

openapi: 3.1.0
info:
  title: Test 2
  version: "1.0.0"
  description: Test 2
components:
  schemas:
    Item:
      title: Item
      type: object
      properties:
        weightUnitOfMeasure:
          $ref: '#/components/schemas/WeightUnitOfMeasure'
    WeightUnitOfMeasure:
      title: Weight Unit of Measure
      type: object
      description: A weight unit of measure
      properties:
        unit:
          type: string
        description:
          type: string

Generation Details

The plugin configuration is the following:

            <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>7.18.0</version>
                <executions>
                      <execution>
                        <id>test-spring</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>
                                src/main/resources/openapi.yaml</inputSpec>
                            <generatorName>spring</generatorName>
                            <apiPackage>spring.api</apiPackage>
                            <modelPackage>spring.model</modelPackage>
                            <modelNamePrefix>Spring</modelNamePrefix>
                            <modelNameSuffix>Model</modelNameSuffix>
                            <configOptions>
                                <useSpringBoot3>true</useSpringBoot3>
                                <openApiNullable>false</openApiNullable>
                                <interfaceOnly>true</interfaceOnly>
                            </configOptions>
                        </configuration>
                    </execution>
                    <execution>
                        <id>test-java</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>
                                src/main/resources/openapi.yaml</inputSpec>
                            <generatorName>java</generatorName>
                            <apiPackage>java.api</apiPackage>
                            <modelPackage>java.model</modelPackage>
                            <modelNamePrefix>Java</modelNamePrefix>
                            <modelNameSuffix>Model</modelNameSuffix>
                            <configOptions>
                                <library>restclient</library>
                                <annotationLibrary>none</annotationLibrary>
                                <openApiNullable>false</openApiNullable>
                                <generateBuilders>true</generateBuilders>
                                <useJakartaEe>true</useJakartaEe>
                            </configOptions>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

Steps to reproduce

After running, you will notice it will only create 2 model files with both the spring and java generators.

• java
  • JavaItemModel
  • JavaListItems200ResponseModel
• spring
  • SpringItemModel
  • SpringListItems200ResponseModel

But you would expect it to make models for each unique item and multiple response models.

Use openapi.yaml with test1.yaml and test2.yaml and the provided Maven plugin configuration to reproduce the Java and Spring outputs. Compare the generated model sets with the expected distinct referenced models and response models, then trace external-reference and model-name handling and add a regression test for the collision.