Spring Web Reactive | 2. WebClient | 2.4. Request Body

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Encode a request body from any asynchronous type handled by ReactiveAdapterRegistry, such as Mono or Kotlin coroutine Deferred.

Mono<Void> result = client.post()
        .uri("/persons/{id}", id)
        .contentType(MediaType.APPLICATION_JSON)
        .body(personMono, Person.class)
        .retrieve()
        .bodyToMono(Void.class);

Encode a stream of objects in the same way. For an actual value, use bodyValue.

Mono<Void> result = client.post()
        .uri("/persons/{id}", id)
        .contentType(MediaType.APPLICATION_JSON)
        .bodyValue(person)
        .retrieve()
        .bodyToMono(Void.class);

2.4.1. Form Data

Provide MultiValueMap<String, String> as the body. FormHttpMessageWriter automatically sets the content type to application/x-www-form-urlencoded.

Mono<Void> result = client.post()
        .uri("/path", id)
        .bodyValue(formData)
        .retrieve()
        .bodyToMono(Void.class);

Use BodyInserters for inline form data.

.body(fromFormData("k1", "v1").with("k2", "v2"))

2.4.2. Multipart Data

Provide a MultiValueMap<String, ?> whose values are part content objects or HttpEntity instances containing part content and headers. MultipartBodyBuilder offers a convenient API.

MultipartBodyBuilder builder = new MultipartBodyBuilder();
builder.part("fieldPart", "fieldValue");
builder.part("filePart1", new FileSystemResource("...logo.png"));
builder.part("jsonPart", new Person("Jason"));
builder.part("myPart", part);

MultiValueMap<String, HttpEntity<?>> parts = builder.build();

Part content types are usually selected automatically from the chosen HttpMessageWriter or a Resource file extension. Use an overloaded part method to set a MediaType explicitly when required.

Mono<Void> result = client.post()
        .uri("/path", id)
        .body(builder.build())
        .retrieve()
        .bodyToMono(Void.class);

When using MultipartBodyBuilder, the HttpEntity wrappers ensure multipart handling. You can also provide inline multipart content with BodyInserters.

.body(fromMultipartData("fieldPart", "value").with("filePart", resource))