Is there a swagger-codegen extension that generates asynchttp clients in java?

Question

I am trying to use swagger-codegen for the first time to automatically generate java clients for my REST service. I downloaded the the cli and ran this command:

java -jar ~/Downloads/swagger-codegen-cli-2.2.1.jar generate \
    -i http://my.services.url/swagger.json \
    -l java

The code that this generated used okhttp client implementation. I'd really like to leverage CompletableFutures, but that seems well beyond what swagger provides. Does anyone know of a way to generate an asynchttp client from swagger codegen? Is this a solved problem or would it require extension of the source code via the DefaultCodegen?