Spring Web Reactive | 2. WebClient | 2.8. Synchronous Use

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You can use WebClient in a synchronous style by blocking at the end for the result.

Java

Person person = client.get().uri("/person/{id}", i).retrieve()
    .bodyToMono(Person.class)
    .block();

List<Person> persons = client.get().uri("/persons").retrieve()
    .bodyToFlux(Person.class)
    .collectList()
    .block();

Kotlin

val person = runBlocking {
    client.get().uri("/person/{id}", i).retrieve()
            .awaitBody<Person>()
}

val persons = runBlocking {
    client.get().uri("/persons").retrieve()
            .bodyToFlow<Person>()
            .toList()
}

However, if you need to make multiple calls, it is more efficient to wait for the combined result instead of blocking on each response separately.

Java

Mono<Person> personMono = client.get().uri("/person/{id}", personId)
        .retrieve().bodyToMono(Person.class);

Mono<List<Hobby>> hobbiesMono = client.get().uri("/person/{id}/hobbies", personId)
        .retrieve().bodyToFlux(Hobby.class).collectList();

Map<String, Object> data = Mono.zip(personMono, hobbiesMono, (person, hobbies) -> {
            Map<String, String> map = new LinkedHashMap<>();
            map.put("person", person);
            map.put("hobbies", hobbies);
            return map;
        })
        .block();

Kotlin

val data = runBlocking {
        val personDeferred = async {
            client.get().uri("/person/{id}", personId)
                    .retrieve().awaitBody<Person>()
        }

        val hobbiesDeferred = async {
            client.get().uri("/person/{id}/hobbies", personId)
                    .retrieve().bodyToFlow<Hobby>().toList()
        }

        mapOf("person" to personDeferred.await(), "hobbies" to hobbiesDeferred.await())
    }

These are simple examples. Many other patterns and operators can compose reactive pipelines that make multiple remote calls.

There is no need to block in Spring MVC or Spring WebFlux controllers when using Flux and Mono. Simply return the reactive type from the controller method. The same principle applies to Kotlin coroutines and Spring WebFlux: use a suspending function or return a Flow from the controller method.