[BUG][JAVA] Gson truncates Long values for Object

Description

When an endpoint's response type is set to an Object, there are issues de-serializing Long values using Gson in the generated ApiClient class because of the default objectToNumberStrategy that Gson uses. By default Gson uses ToNumberPolicy.DOUBLE. as the objectToNumberStrategy and this is problematic when trying to de-serialize a value that is larger than a double and causes inaccuracies.

openapi-generator version

6.0.1

OpenAPI declaration file content or url

Problematic endpoint where the GET has an Object return type.
https://github.com/candlepin/candlepin/blob/master/api/candlepin-api-spec.yaml#L1122-L1160

Steps to reproduce

1. Define an endpoint that returns an object for GET requests.
2. Generate the java api classes.
3. Use the api class to make the GET request for the endpoint.
4. Return a json with a Long value like the following example.

{"value" : 7076632681529943151}

This example will be de-serialized to:
{value=7.076632681529943E18}

Related issues/PRs

I was unable to find any related open or closed issues/PRs.

Suggest a fix/enhancement

As a suggestion, you could set the Gson objectToNumberStrategy to ToNumberPolicy.LONG_OR_DOUBLE in the generated ApiClient class.

Start with the generated Java ApiClient and reproduce the issue using the candlepin endpoint described in the report, returning the provided JSON value. Inspect the Java generator area that controls Gson deserialization and verify the completed change preserves the Long value without converting it to an imprecise Double.