Migrating RestTemplate code to RestClient code in Spring Boot app

Question

I want to use the Spring Boot's RestClient feature for my application.

So, I want to migrate the existing Spring Boot's RestTemplate code to Spring Boot's RestClient code.

I have a code that works using RestTemplate:

private byte[] request(Data data) {
   HttpHeaders headers = new HttpHeaders();
   headers.setContentType(MediaType.APPLICATION_JSON);
   HttpEntity<ResponseData> entity = new HttpEntity<>(data, headers);
   return restTemplate.exchange(url + uri, HttpMethod.POST, entity, byte[].class).getBody();
}

How can I write equivalent request using Spring Boot's RestClient?

I've tried this:

    private byte[] request(Data data) {
        return restClientBuilder.baseUrl(url)
                .build()
                .post()
                .uri(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .body(data)
                .retrieve()
                .onStatus(HttpStatusCode::isError, new ApiErrorHandler())
                .toEntity(byte[].class).getBody();
    }

This:

    private byte[] request(Data data) {
        return restClientBuilder.baseUrl(url)
                .build()
                .post()
                .uri(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .body(data)
                .retrieve()
                .onStatus(HttpStatusCode::isError, new ApiErrorHandler())
                .body(byte[].class);
    }

This

    private byte[] request(Data data) {
        return restClientBuilder.baseUrl(url)
                .build()
                .post()
                .uri(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .body(data)
                .exchange((request, res) -> res.getBody().readAllBytes());
    }

And this way

    private byte[] requestD(Data data) {
        return restClientBuilder.baseUrl(url)
                .build()
                .post()
                .uri(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .body(data)
                .retrieve()
                .onStatus(HttpStatusCode::isError, new ApiErrorHandler())
                .toEntity(new ParameterizedTypeReference<byte[]>() {
                }).getBody();
    }

And none of these works. Can you help me please ?