[BUG][JAVA] Generating client library with retrofit2, creates incorrect documentation/code

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used? 4.2.3
• Have you search for related issues/PRs?
• What's the actual output vs expected output? Incorrect Documentation or code

Description

For given open-api spec, when generating client code for Retrofit2 library,
The generated code or documentation is incorrect.

There are methods/classes missing or the generated markdown documentation is incorrect.

openapi-generator version

Using Generator version 4.2.3 installed via homebrew

OpenAPI declaration file content or url

Using the below fromParameter.yaml spec file, I am generating a retrofit2 based client library

openapi: 3.0.0
servers:
  - url: "localhost:8080"
info:
  version: 1.0.0
  title: OpenAPI Petstore
  license:
    name: Apache-2.0
    url: "https://www.apache.org/licenses/LICENSE-2.0.html"
paths:
  /get_path_style:
    get:
      operationId: getFormStyleParamMethod
      parameters:
        - in: query
          name: styleQPName
          style: form
          schema:
            type: object
            properties:
              queryParmObjField1:
                type: string
      responses:
        "200":
          description: OK
  /get_path_explode:
    get:
      operationId: getExplodingParmMethod
      parameters:
        - in: query
          name: explodingQPName
          style: form
          explode: true
          schema:
            type: object
            properties:
              queryParamObjExplodedField1:
                type: string
      responses:
        "200":
          description: OK

This generates Documentation in docs folder with a file DefaultApi.md and the details for usage shows the sample as below but that is incorrect

// Import classes:
import org.openapitools.client.ApiClient;
import org.openapitools.client.ApiException;
import org.openapitools.client.Configuration;
import org.openapitools.client.models.*;
import org.openapitools.client.api.DefaultApi;

public class Example {
    public static void main(String[] args) {
        ApiClient defaultClient = Configuration.getDefaultApiClient();
        defaultClient.setBasePath("http://localhost:8080");

        DefaultApi apiInstance = new DefaultApi(defaultClient);
        ExplodingQPName explodingQPName = new ExplodingQPName(); // ExplodingQPName | 
        try {
            apiInstance.getExplodingParmMethod(explodingQPName);
        } catch (ApiException e) {
            System.err.println("Exception when calling DefaultApi#getExplodingParmMethod");
            System.err.println("Status code: " + e.getCode());
            System.err.println("Reason: " + e.getResponseBody());
            System.err.println("Response headers: " + e.getResponseHeaders());
            e.printStackTrace();
        }
    }
}

• There is NO Configuration.java class generated
• There is no method setBasePath(String urlbase) method present on APIClient.java class

Command line used for generation

openapi-generator generate -i fromParameter.yaml -c codegen-config.json -g java -o sources/clients/java/

the codegen-config.json is as follows

{
  "dateLibrary": "java8",
  "delegatePattern": true,
  "hideGenerationTimestamp": true,
  "java8": true,
  "library": "retrofit2"
}

Language - Java
Library - Retrofit2

Steps to reproduce

Related issues/PRs

Suggest a fix

Start with the supplied fromParameter.yaml and codegen-config.json, then run the shown openapi-generator command with the Retrofit2 library. Compare docs/DefaultApi.md with the generated APIClient.java and check the reported absence of Configuration.java and setBasePath(String urlbase). Done means the generated documentation matches the available Java API and the expected classes or methods are present.