[REQ] Adding 'implements' or 'extends' to a Java class without changing the OpenApi.yaml.

Is your feature request related to a problem? Please describe.

I have some Java classes, ExampleClass1 and ExampleClass2.
They are basically the same, except for a few different variables.

I would like to add an interface or a parent class to them without changing the OpenAPI.yaml.

I get the OpenAPI.yaml from a different endpoint, and I don't want to change anything there.

Describe the solution you'd like

My goal is to add an option to the config that would add an interface to specific classes.

A config like this:

addImplements: {
ExampleClass1: "com.test.project.CommonInterface",
ExampleClass2: "com.test.project.CommonInterface"
}

So, I would not have to change the original OpenAPI.yaml, and I could generate the classes with the interface automatically.

Describe alternatives you've considered

An alternative would be to use a config to add an external parent.

addExtends: {
ExampleClass1: "com.test.project.CommonParent",
ExampleClass2: "com.test.project.CommonParent"
}

Additional context

Some Examples:

my OpenAPi.yaml

// 20231004115458
// http://localhost:8084/v3/api-docs

{
  "openapi": "3.0.1",
  "info": {
    "title": "OpenAPI definition",
    "version": "v0"
  },
  "servers": [
    {
      "url": "http://localhost:8084",
      "description": "Generated server url"
    }
  ],
  "paths": {
    "/exampleClass2": {
      "post": {
        "tags": [
          "basic-controller"
        ],
        "operationId": "postDataForm",
        "requestBody": {
          "content": {
            "application/x-www-form-urlencoded": {
              "schema": {
                "$ref": "#/components/schemas/ExampleClass2"
              }
            }
          },
          "required": true
        },
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "*/*": {
                "schema": {
                  "$ref": "#/components/schemas/ExampleClass2"
                }
              }
            }
          }
        }
      }
    },
    "/exampleClass1": {
      "post": {
        "tags": [
          "basic-controller"
        ],
        "operationId": "postDataForm_1",
        "requestBody": {
          "content": {
            "application/x-www-form-urlencoded": {
              "schema": {
                "$ref": "#/components/schemas/ExampleClass1"
              }
            }
          },
          "required": true
        },
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "*/*": {
                "schema": {
                  "$ref": "#/components/schemas/ExampleClass1"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "ExampleClass2": {
        "type": "object",
        "properties": {
          "version": {
            "type": "string"
          },
          "id": {
            "type": "integer",
            "format": "int32"
          },
          "exampleDouble": {
            "type": "number",
            "format": "double"
          }
        }
      },
      "ExampleClass1": {
        "type": "object",
        "properties": {
          "version": {
            "type": "string"
          },
          "id": {
            "type": "integer",
            "format": "int32"
          },
          "somethingDifferent": {
            "type": "string"
          }
        }
      }
    }
  }
}

/**
 * ExampleClass1
 */

@Generated(value = "org.openapitools.codegen.languages.SpringCodegen")
public class ExampleClass1 {

  private String version;
  private Integer id;
  private String somethingDifferent;

...
}

/**
 * ExampleClass2
 */

@Generated(value = "org.openapitools.codegen.languages.SpringCodegen")
public class ExampleClass2 {

  private String version;
  private Integer id;
  private Double exampleDouble;

...
}

How i want them to be generated:

public class ExampleClass1 implements CommonInterface {
...
}

public class ExampleClass2 implements CommonInterface {
...
}

Or as Parent

public class ExampleClass1 extends CommonParent{
...
}

public class ExampleClass2 extends CommonParent{
...
}

No source files, tests, or entry points are identified in the issue. Start by locating the Java generator's configuration handling and model-class generation path, then define how per-class implements or extends settings should be represented and validated; done means generated classes include the requested relationship without requiring changes to the OpenAPI document.