[REQ] CompletableFuture implementation of ApiCallback?

Is your feature request related to a problem? Please describe.

This is regarding the Java client.

The problem is one of expressiveness. I'm using the generator pretty heavily in a few projects and want to utilize the async methods, but am concerned about how much more bootstrapping it'll take to make my calls asynchronous.

Describe the solution you'd like

Would be nice to have a call back implementation already in the generated api class with an option to write async methods like so:

contactApi.getContactAsync(id)
  .thenApply(contact -> {
    LOG.info("Received contact: {}", contact);
  });

Describe alternatives you've considered

We've considered writing our own ApiCallBack future implementation, but it still doesn't read as well as if the implementation was baked into the generated api class.

// Implementation
class ApiCallBackImpl<T> implements ApiCallback<T> {
  ...
  public CompletionStage<T> getFuture() {} // returns future
}

// Usage
ApiCallBackImpl<Contact> callback = new ApiCallBackImpl<>();
contactApi.getContactAsync(id, callback);

callback.getFuture()
  .thenApply(contact -> {
    LOG.info("Received contact: {}", contact);
  });

Additional context

CompletableFuture would not offer ability to track upload/download progress, but I think a majority of usecases would not require that.

Would appreciate any thoughts on this.

Start by reviewing the Java client’s generated API classes and the existing ApiCallback async methods. Compare the requested CompletableFuture or CompletionStage usage with the current callback flow and consider the stated limitation around upload and download progress. Done means the generator can optionally produce async methods supporting the proposed future-based usage without removing callback functionality.