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

[ShahBinoy]

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

[wing328]

@ShahBinoy thanks for reporting the issue. May I know if you've time to contribute the fix? I can show you some good starting points.

[ShahBinoy]

@wing328 I can try, Please guide me through the starting points