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