# WebFlux Support

## WebFlux Support

The WebFlux Spring Integration module (`spring-integration-webflux`) allows for the execution of HTTP requests and the processing of inbound HTTP requests in a reactive manner.

You need to include this dependency into your project:

Maven

```
<dependency>
    <groupId>org.springframework.integration</groupId>
    <artifactId>spring-integration-webflux</artifactId>
    <version>5.5.9</version>
</dependency>
```

Gradle

```
compile "org.springframework.integration:spring-integration-webflux:5.5.9"
```

The `io.projectreactor.netty:reactor-netty` dependency must be included in case of non-Servlet-based server configuration.

The WebFlux support consists of the following gateway implementations: `WebFluxInboundEndpoint` and `WebFluxRequestExecutingMessageHandler`.
The support is fully based on the Spring [WebFlux](https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#spring-webflux) and [Project Reactor](https://projectreactor.io/) foundations.
See [HTTP Support](./http.html#http) for more information, since many options are shared between reactive and regular HTTP components.

### WebFlux Namespace Support

Spring Integration provides a `webflux` namespace and the corresponding schema definition.
To include it in your configuration, add the following namespace declaration in your application context configuration file:

```
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:int="http://www.springframework.org/schema/integration"
  xmlns:int-webflux="http://www.springframework.org/schema/integration/webflux"
  xsi:schemaLocation="
    http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/integration
    https://www.springframework.org/schema/integration/spring-integration.xsd
    http://www.springframework.org/schema/integration/webflux
    https://www.springframework.org/schema/integration/webflux/spring-integration-webflux.xsd">
    ...
</beans>
```

### WebFlux Inbound Components

Starting with version 5.0, the `WebFluxInboundEndpoint` implementation of `WebHandler` is provided.
This component is similar to the MVC-based `HttpRequestHandlingEndpointSupport`, with which it shares some common options through the newly extracted `BaseHttpInboundEndpoint`.
It is used in the Spring WebFlux reactive environment (instead of MVC).
The following example shows a simple implementation of a WebFlux endpoint:

Java DSL

```
@Bean
public IntegrationFlow inboundChannelAdapterFlow() {
    return IntegrationFlows
        .from(WebFlux.inboundChannelAdapter("/reactivePost")
            .requestMapping(m -> m.methods(HttpMethod.POST))
            .requestPayloadType(ResolvableType.forClassWithGenerics(Flux.class, String.class))
            .statusCodeFunction(m -> HttpStatus.ACCEPTED))
        .channel(c -> c.queue("storeChannel"))
        .get();
}
```

Kotlin DSL

```
@Bean
fun inboundChannelAdapterFlow() =
    integrationFlow(
        WebFlux.inboundChannelAdapter("/reactivePost")
            .apply {
                requestMapping { m -> m.methods(HttpMethod.POST) }
                requestPayloadType(ResolvableType.forClassWithGenerics(Flux::class.java, String::class.java))
                statusCodeFunction { m -> HttpStatus.ACCEPTED }
            })
    {
        channel { queue("storeChannel") }
    }
```

Java

```
@Configuration
@EnableWebFlux
@EnableIntegration
public class ReactiveHttpConfiguration {

    @Bean
    public WebFluxInboundEndpoint simpleInboundEndpoint() {
        WebFluxInboundEndpoint endpoint = new WebFluxInboundEndpoint();
        RequestMapping requestMapping = new RequestMapping();
        requestMapping.setPathPatterns("/test");
        endpoint.setRequestMapping(requestMapping);
        endpoint.setRequestChannelName("serviceChannel");
        return endpoint;
    }

    @ServiceActivator(inputChannel = "serviceChannel")
    String service() {
        return "It works!";
    }

}
```

XML

```
<int-webflux:inbound-gateway request-channel="requests" path="/sse">
    <int-webflux:request-mapping produces="text/event-stream"/>
</int-webflux:inbound-gateway>
```

The configuration is similar to the `HttpRequestHandlingEndpointSupport` (mentioned prior to the example), except that we use `@EnableWebFlux` to add the WebFlux infrastructure to our integration application.
Also, the `WebFluxInboundEndpoint` performs `sendAndReceive` operations to the downstream flow by using back-pressure, on-demand based capabilities, provided by the reactive HTTP server implementation.

|   |The reply part is non-blocking as well and is based on the internal `FutureReplyChannel`, which is flat-mapped to a reply `Mono` for on-demand resolution.|
|---|----------------------------------------------------------------------------------------------------------------------------------------------------------|

You can configure the `WebFluxInboundEndpoint` with a custom `ServerCodecConfigurer`, a `RequestedContentTypeResolver`, and even a `ReactiveAdapterRegistry`.
The latter provides a mechanism you can use to return a reply as any reactive type: Reactor `Flux`, RxJava `Observable`, `Flowable`, and others.
This way, we can implement [Server Sent Events](https://en.wikipedia.org/wiki/Server-sent_events) scenarios with Spring Integration components, as the following example shows:

Java DSL

```
@Bean
public IntegrationFlow sseFlow() {
    return IntegrationFlows
            .from(WebFlux.inboundGateway("/sse")
                    .requestMapping(m -> m.produces(MediaType.TEXT_EVENT_STREAM_VALUE)))
            .handle((p, h) -> Flux.just("foo", "bar", "baz"))
            .get();
}
```

Kotlin DSL

```
@Bean
fun sseFlow() =
     integrationFlow(
            WebFlux.inboundGateway("/sse")
                       .requestMapping(m -> m.produces(MediaType.TEXT_EVENT_STREAM_VALUE)))
            {
                 handle { (p, h) -> Flux.just("foo", "bar", "baz") }
            }
```

Java

```
@Bean
public WebFluxInboundEndpoint webfluxInboundGateway() {
    WebFluxInboundEndpoint endpoint = new WebFluxInboundEndpoint();
    RequestMapping requestMapping = new RequestMapping();
    requestMapping.setPathPatterns("/sse");
    requestMapping.setProduces(MediaType.TEXT_EVENT_STREAM_VALUE);
    endpoint.setRequestMapping(requestMapping);
    endpoint.setRequestChannelName("requests");
    return endpoint;
}
```

XML

```
<int-webflux:inbound-channel-adapter id="reactiveFullConfig" channel="requests"
                               path="test1"
                               auto-startup="false"
                               phase="101"
                               request-payload-type="byte[]"
                               error-channel="errorChannel"
                               payload-expression="payload"
                               supported-methods="PUT"
                               status-code-expression="'202'"
                               header-mapper="headerMapper"
                               codec-configurer="codecConfigurer"
                               reactive-adapter-registry="reactiveAdapterRegistry"
                               requested-content-type-resolver="requestedContentTypeResolver">
            <int-webflux:request-mapping headers="foo"/>
            <int-webflux:cross-origin origin="foo" method="PUT"/>
            <int-webflux:header name="foo" expression="'foo'"/>
</int-webflux:inbound-channel-adapter>
```

See [Request Mapping Support](./http.html#http-request-mapping) and [Cross-origin Resource Sharing (CORS) Support](./http.html#http-cors) for more possible configuration options.

When the request body is empty or `payloadExpression` returns `null`, the request params (`MultiValueMap<String, String>`) is used for a `payload` of the target message to process.

#### Payload Validation

Starting with version 5.2, the `WebFluxInboundEndpoint` can be configured with a `Validator`.
Unlike the MVC validation in the [HTTP Support](./http.html#http-validation), it is used to validate elements in the `Publisher` to which a request has been converted by the `HttpMessageReader`, before performing a fallback and `payloadExpression` functions.
The Framework can’t assume how complex the `Publisher` object can be after building the final payload.
If there is a requirements to restrict validation visibility for exactly final payload (or its `Publisher` elements), the validation should go downstream instead of WebFlux endpoint.
See more information in the Spring WebFlux [documentation](https://docs.spring.io/spring/docs/5.1.8.RELEASE/spring-framework-reference/web-reactive.html#webflux-fn-handler-validation).
An invalid payload is rejected with an `IntegrationWebExchangeBindException` (a `WebExchangeBindException` extension), containing all the validation `Errors`.
See more in Spring Framework [Reference Manual](https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation) about validation.

### WebFlux Outbound Components

The `WebFluxRequestExecutingMessageHandler` (starting with version 5.0) implementation is similar to `HttpRequestExecutingMessageHandler`.
It uses a `WebClient` from the Spring Framework WebFlux module.
To configure it, define a bean similar to the following:

Java DSL

```
@Bean
public IntegrationFlow outboundReactive() {
    return f -> f
        .handle(WebFlux.<MultiValueMap<String, String>>outboundGateway(m ->
                UriComponentsBuilder.fromUriString("http://localhost:8080/foo")
                        .queryParams(m.getPayload())
                        .build()
                        .toUri())
                .httpMethod(HttpMethod.GET)
                .expectedResponseType(String.class));
}
```

Kotlin DSL

```
@Bean
fun outboundReactive() =
    integrationFlow {
        handle(
            WebFlux.outboundGateway<MultiValueMap<String, String>>({ m ->
                UriComponentsBuilder.fromUriString("http://localhost:8080/foo")
                    .queryParams(m.getPayload())
                    .build()
                    .toUri()
            })
                .httpMethod(HttpMethod.GET)
                .expectedResponseType(String::class.java)
        )
    }
```

Java

```
@ServiceActivator(inputChannel = "reactiveHttpOutRequest")
@Bean
public WebFluxRequestExecutingMessageHandler reactiveOutbound(WebClient client) {
    WebFluxRequestExecutingMessageHandler handler =
        new WebFluxRequestExecutingMessageHandler("http://localhost:8080/foo", client);
    handler.setHttpMethod(HttpMethod.POST);
    handler.setExpectedResponseType(String.class);
    return handler;
}
```

XML

```
<int-webflux:outbound-gateway id="reactiveExample1"
    request-channel="requests"
    url="http://localhost/test"
    http-method-expression="headers.httpMethod"
    extract-request-payload="false"
    expected-response-type-expression="payload"
    charset="UTF-8"
    reply-timeout="1234"
    reply-channel="replies"/>

<int-webflux:outbound-channel-adapter id="reactiveExample2"
    url="http://localhost/example"
    http-method="GET"
    channel="requests"
    charset="UTF-8"
    extract-payload="false"
    expected-response-type="java.lang.String"
    order="3"
    auto-startup="false"/>
```

The `WebClient` `exchange()` operation returns a `Mono<ClientResponse>`, which is mapped (by using several `Mono.map()` steps) to an `AbstractIntegrationMessageBuilder` as the output from the `WebFluxRequestExecutingMessageHandler`.
Together with the `ReactiveChannel` as an `outputChannel`, the `Mono<ClientResponse>` evaluation is deferred until a downstream subscription is made.
Otherwise, it is treated as an `async` mode, and the `Mono` response is adapted to a `SettableListenableFuture` for an asynchronous reply from the `WebFluxRequestExecutingMessageHandler`.
The target payload of the output message depends on the `WebFluxRequestExecutingMessageHandler` configuration.
The `setExpectedResponseType(Class<?>)` or `setExpectedResponseTypeExpression(Expression)` identifies the target type of the response body element conversion.
If `replyPayloadToFlux` is set to `true`, the response body is converted to a `Flux` with the provided `expectedResponseType` for each element, and this `Flux` is sent as the payload downstream.
Afterwards, you can use a [splitter](./splitter.html#splitter) to iterate over this `Flux` in a reactive manner.

In addition a `BodyExtractor<?, ClientHttpResponse>` can be injected into the `WebFluxRequestExecutingMessageHandler` instead of the `expectedResponseType` and `replyPayloadToFlux` properties.
It can be used for low-level access to the `ClientHttpResponse` and more control over body and HTTP headers conversion.
Spring Integration provides `ClientHttpResponseBodyExtractor` as a identity function to produce (downstream) the whole `ClientHttpResponse` and any other possible custom logic.

Starting with version 5.2, the `WebFluxRequestExecutingMessageHandler` supports reactive `Publisher`, `Resource`, and `MultiValueMap` types as the request message payload.
A respective `BodyInserter` is used internally to be populated into the `WebClient.RequestBodySpec`.
When the payload is a reactive `Publisher`, a configured `publisherElementType` or `publisherElementTypeExpression` can be used to determine a type for the publisher’s element type.
The expression must be resolved to a `Class<?>`, `String` which is resolved to the target `Class<?>` or `ParameterizedTypeReference`.

Starting with version 5.5, the `WebFluxRequestExecutingMessageHandler` exposes an `extractResponseBody` flag (which is `true` by default) to return just the response body, or to return the whole `ResponseEntity` as the reply message payload, independently of the provided `expectedResponseType` or `replyPayloadToFlux`.
If a body is not present in the `ResponseEntity`, this flag is ignored and the whole `ResponseEntity` is returned.

See [HTTP Outbound Components](./http.html#http-outbound) for more possible configuration options.

### WebFlux Header Mappings

Since WebFlux components are fully based on the HTTP protocol, there is no difference in the HTTP headers mapping.
See [HTTP Header Mappings](./http.html#http-header-mapping) for more possible options and components to use for mapping headers.
