spring-framework/framework-docs/modules/ROOT/pages/web/webflux-webclient/client-body.adoc

[[webflux-client-body]]
= Request Body

The request body can be encoded from any asynchronous type handled by `ReactiveAdapterRegistry`,
like `Mono` or Kotlin Coroutines `Deferred` as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	Mono<Person> personMono = ... ;

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val personDeferred: Deferred<Person> = ...

	client.post()
			.uri("/persons/{id}", id)
			.contentType(MediaType.APPLICATION_JSON)
			.body<Person>(personDeferred)
			.retrieve()
			.awaitBody<Unit>()
----
======

You can also have a stream of objects be encoded, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	Flux<Person> personFlux = ... ;

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val people: Flow<Person> = ...

	client.post()
			.uri("/persons/{id}", id)
			.contentType(MediaType.APPLICATION_JSON)
			.body(people)
			.retrieve()
			.awaitBody<Unit>()
----
======

Alternatively, if you have the actual value, you can use the `bodyValue` shortcut method,
as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	Person person = ... ;

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val person: Person = ...

	client.post()
			.uri("/persons/{id}", id)
			.contentType(MediaType.APPLICATION_JSON)
			.bodyValue(person)
			.retrieve()
			.awaitBody<Unit>()
----
======


[[webflux-client-body-form]]
== Form Data

To send form data, you can provide a `MultiValueMap<String, String>` as the body. Note that the
content is automatically set to `application/x-www-form-urlencoded` by the
`FormHttpMessageWriter`. The following example shows how to use `MultiValueMap<String, String>`:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	MultiValueMap<String, String> formData = ... ;

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val formData: MultiValueMap<String, String> = ...

	client.post()
			.uri("/path", id)
			.bodyValue(formData)
			.retrieve()
			.awaitBody<Unit>()
----
======

You can also supply form data in-line by using `BodyInserters`, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	import static org.springframework.web.reactive.function.BodyInserters.*;

	Mono<Void> result = client.post()
			.uri("/path", id)
			.body(fromFormData("k1", "v1").with("k2", "v2"))
			.retrieve()
			.bodyToMono(Void.class);
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	import org.springframework.web.reactive.function.BodyInserters.*

	client.post()
			.uri("/path", id)
			.body(fromFormData("k1", "v1").with("k2", "v2"))
			.retrieve()
			.awaitBody<Unit>()
----
======


[[webflux-client-body-multipart]]
== Multipart Data

To send multipart data, you need to provide a `MultiValueMap<String, ?>` whose values are
either `Object` instances that represent part content or `HttpEntity` instances that represent the content and
headers for a part. `MultipartBodyBuilder` provides a convenient API to prepare a
multipart request. The following example shows how to create a `MultiValueMap<String, ?>`:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	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); // Part from a server request

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val builder = MultipartBodyBuilder().apply {
		part("fieldPart", "fieldValue")
		part("filePart1", FileSystemResource("...logo.png"))
		part("jsonPart", Person("Jason"))
		part("myPart", part) // Part from a server request
	}

	val parts = builder.build()
----
======

In most cases, you do not have to specify the `Content-Type` for each part. The content
type is determined automatically based on the `HttpMessageWriter` chosen to serialize it
or, in the case of a `Resource`, based on the file extension. If necessary, you can
explicitly provide the `MediaType` to use for each part through one of the overloaded
builder `part` methods.

Once a `MultiValueMap` is prepared, the easiest way to pass it to the `WebClient` is
through the `body` method, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	MultipartBodyBuilder builder = ...;

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

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val builder: MultipartBodyBuilder = ...

	client.post()
			.uri("/path", id)
			.body(builder.build())
			.retrieve()
			.awaitBody<Unit>()
----
======

If the `MultiValueMap` contains at least one non-`String` value, which could also
represent regular form data (that is, `application/x-www-form-urlencoded`), you need not
set the `Content-Type` to `multipart/form-data`. This is always the case when using
`MultipartBodyBuilder`, which ensures an `HttpEntity` wrapper.

As an alternative to `MultipartBodyBuilder`, you can also provide multipart content,
inline-style, through the built-in `BodyInserters`, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	import static org.springframework.web.reactive.function.BodyInserters.*;

	Mono<Void> result = client.post()
			.uri("/path", id)
			.body(fromMultipartData("fieldPart", "value").with("filePart", resource))
			.retrieve()
			.bodyToMono(Void.class);
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	import org.springframework.web.reactive.function.BodyInserters.*

	client.post()
			.uri("/path", id)
			.body(fromMultipartData("fieldPart", "value").with("filePart", resource))
			.retrieve()
			.awaitBody<Unit>()
----
======

[[partevent]]
=== `PartEvent`

To stream multipart data sequentially, you can provide multipart content through `PartEvent`
objects.

- Form fields can be created via `FormPartEvent::create`.
- File uploads can be created via `FilePartEvent::create`.

You can concatenate the streams returned from methods via `Flux::concat`, and create a request for
the `WebClient`.

For instance, this sample will POST a multipart form containing a form field and a file.

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	Resource resource = ...
	Mono<String> result = webClient
		.post()
		.uri("https://example.com")
		.body(Flux.concat(
				FormPartEvent.create("field", "field value"),
				FilePartEvent.create("file", resource)
		), PartEvent.class)
		.retrieve()
		.bodyToMono(String.class);
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	var resource: Resource = ...
	var result: Mono<String> = webClient
		.post()
		.uri("https://example.com")
		.body(
			Flux.concat(
				FormPartEvent.create("field", "field value"),
				FilePartEvent.create("file", resource)
			)
		)
		.retrieve()
		.bodyToMono()
----
======

On the server side, `PartEvent` objects that are received via `@RequestBody` or
`ServerRequest::bodyToFlux(PartEvent.class)` can be relayed to another service
via the `WebClient`.