리액티브 호출을 위한 WebClient

What is WebClient

Building a WebClient

WebClient client = WebClient.builder()
    .baseUrl("https://api.example.com")
    .build();

A Simple GET

Mono<User> user = client.get()
    .uri("/users/{id}", 1)
    .retrieve()
    .bodyToMono(User.class);
user.subscribe(System.out::println);

Fetching a Collection

Flux<User> users = client.get()
    .uri("/users")
    .retrieve()
    .bodyToFlux(User.class);

Sending a POST Body

Mono<User> created = client.post()
    .uri("/users")
    .bodyValue(new User("Alice"))
    .retrieve()
    .bodyToMono(User.class);

Adding Headers

Mono<String> result = client.get()
    .uri("/data")
    .header("Authorization", "Bearer token123")
    .retrieve()
    .bodyToMono(String.class);

Handling Error Statuses

Mono<User> user = client.get()
    .uri("/users/{id}", 99)
    .retrieve()
    .onStatus(HttpStatusCode::is4xxClientError,
        resp -> Mono.error(new RuntimeException("Not found")))
    .bodyToMono(User.class);

Composing Calls with flatMap

Mono<Order> order = client.get()
    .uri("/users/{id}", 1)
    .retrieve()
    .bodyToMono(User.class)
    .flatMap(u -> client.get()
        .uri("/orders?userId={id}", u.getId())
        .retrieve()
        .bodyToMono(Order.class));

Timeouts

Mono<User> user = client.get()
    .uri("/users/1")
    .retrieve()
    .bodyToMono(User.class)
    .timeout(Duration.ofSeconds(3));

Retrying on Failure

Mono<User> user = client.get()
    .uri("/users/1")
    .retrieve()
    .bodyToMono(User.class)
    .retry(2);

Registering as a Bean

@Bean
public WebClient webClient() {
    return WebClient.builder()
        .baseUrl("https://api.example.com")
        .build();
}

Quick Check

Recap