@SuppressWarnings("unchecked")
    @UnstableApi
    public <U> TransformingRequestPreparation<T, U> as(ResponseAs<R, U> responseAs) {
        requireNonNull(responseAs, "responseAs");
        this.responseAs = (ResponseAs<T, R>) this.responseAs.andThen(responseAs);
        return (TransformingRequestPreparation<T, U>) this;
    }
Sets the specified {@link ResponseAs} that converts the {@code T} type object into another.
core/src/main/java/com/linecorp/armeria/client/TransformingRequestPreparation.java