@UnstableApi
    public <U> TransformingRequestPreparation<AggregatedHttpResponse, U> as(
            ResponseAs<AggregatedHttpResponse, U> responseAs) {
        requireNonNull(responseAs, "responseAs");
        return new TransformingRequestPreparation<>(this, responseAs);
    }
Sets the specified {@link ResponseAs} that converts the {@link AggregatedHttpResponse} into another.
core/src/main/java/com/linecorp/armeria/client/BlockingWebClientRequestPreparation.java