[Java][Spring] Fix template for reactive implementation with interfaceOnly parameter

[logarithm]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language (Java technical committee: @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger).

Description of the PR

If for java spring-boot template generator we combine reactive and interfaceOnly properties then openapi generator generates incorrect code.

Example without fix:

default Mono<ResponseEntity<ResponseWrapper>> _methodName(@ApiParam(value = ""  )  @Valid @RequestBody Mono<RequestWrapper> requestWrapper, ServerWebExchange exchange) {
    return methodName(requestWrapper);
}

// Override this method
default Mono<ResponseEntity<ResponseWrapper>> methodName(RequestWrapper requestWrapper, ServerWebExchange exchange) {
    Mono<Void> result = Mono.empty();
    exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
    for (MediaType mediaType : exchange.getRequest().getHeaders().getAccept()) {
        if (mediaType.isCompatibleWith(MediaType.valueOf("application/json"))) {
            result = ApiUtil.getExampleResponse(exchange, "");
            break;
        }
    }
    return result.then(Mono.empty());
}

There are multiple problems:

1. Interface method passes incorrect parameter list to delegate.
2. First parameter type of delegate method is incorrect.

After template fix applied:

default Mono<ResponseEntity<ResponseWrapper>> _methodName(@ApiParam(value = ""  )  @Valid @RequestBody Mono<RequestWrapper> requestWrapper, ServerWebExchange exchange) {
    return methodName(requestWrapper, exchange);
}

// Override this method
default Mono<ResponseEntity<ResponseWrapper>> methodName(Mono<RequestWrapper> requestWrapper, ServerWebExchange exchange) {
    Mono<Void> result = Mono.empty();
    exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
    for (MediaType mediaType : exchange.getRequest().getHeaders().getAccept()) {
        if (mediaType.isCompatibleWith(MediaType.valueOf("application/json"))) {
            result = ApiUtil.getExampleResponse(exchange, "");
            break;
        }
    }
    return result.then(Mono.empty());
}

[logarithm]

AppVeyor integration fails because it couldn't clone repo. Unfortunately, I don't have restart button. Could anyone please with permissions re-run AppVeyor build?

[wing328]

@logarithm thanks for the PR. I've restarted the job. (AppVeyor CI covers C# related code)

If no one has further question/feedback on this PR, I'll merge it tomorrow (Tue)

[logarithm]

@wing328 thanks a lot!