[Java] Documentation examples generated by api_doc.mustache for feign, resttemplate, retrofit, retrofit2, google-api-client, rest-assured are incorrect

Description

Because of this code snippet in the JavaClientCodegen.java, ApiException.java is not generated for the feign, resttemplate, retrofit, retrofit2, google-api-client, and rest-assured libraries.

https://github.com/swagger-api/swagger-codegen/blob/9a1460aba1a08ea3095e191caf156c666721feae/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/JavaClientCodegen.java#L206-L211

The generated documentation examples that use ApiException are invalid. For example,

Source:

// Import classes:
//import io.swagger.client.ApiException;
//import io.swagger.client.api.AnotherFakeApi;


AnotherFakeApi apiInstance = new AnotherFakeApi();
Client body = new Client(); // Client | client model
try {
    Client result = apiInstance.testSpecialTags(body);
    System.out.println(result);
} catch (ApiException e) {
    System.err.println("Exception when calling AnotherFakeApi#testSpecialTags");
    e.printStackTrace();
}

This code will not run because ApiException is not a generated class.

Furthermore, the AnotherFakeAPi, is not a class, but instead an interface in retrofit. Thus, the generic api_doc.mustache template does not apply for this framework.

Swagger-codegen version

3.0.20. Based on the repository, version 2 has the same problem.

Steps to reproduce

Repository provides an example of this issue: https://github.com/swagger-api/swagger-codegen/blob/master/samples/client/petstore/java/retrofit2/docs/AnotherFakeApi.md#example

Suggest a fix/enhancement

I would like to write an api_doc.mustache template for these libraries, but I do not know what are the appropriate example code to write now that ApiException isn't a viable class. Is there some other error type for these frameworks?

Start with the referenced JavaClientCodegen.java lines and the api_doc.mustache template, then inspect the generated sample at samples/client/petstore/java/retrofit2/docs/AnotherFakeApi.md and its AnotherFakeApi.java interface. Compare the documentation examples for the listed libraries with their generated APIs. Done means those examples no longer reference an absent ApiException or an inapplicable generic template.