java.net.http.HttpClient

HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create("https://foo.com/"))
        .timeout(Duration.ofMinutes(2))
        .header("Content-Type", "application/json")
        .POST(BodyPublishers.ofFile(Paths.get("file.json")))
        .build();

HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.statusCode());
System.out.println(response.body());  

client.sendAsync(request, BodyHandlers.ofString())
        .thenApply(HttpResponse::body)
        .thenAccept(System.out::println);

import org.springframework.web.client.RestTemplate;

public class RestTemplateExample {
    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        String response = restTemplate.getForObject("https://api.example.com/data", String.class);
        System.out.println(response);
    }
}

import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

public class WebClientExample {
    public static void main(String[] args) {
        WebClient client = WebClient.create("https://api.example.com");

        Mono<String> response = client.get()
                .uri("/data")
                .retrieve()
                .bodyToMono(String.class);

        response.subscribe(System.out::println);
    }
}