This experimental project provides a simple way to try the new Web Reactive support in Spring Framework 5.0.

Go to start.spring.io, set the Spring Boot version to 2.0.0(SNAPSHOT) and add the "Reactive Web" starter.

From there you can take a look at spring-boot-sample-web-reactive in this repository to see examples of reactive @Controllers and the reactive WebClient in use.

By default this Boot Starter uses embedded Tomcat as the default server runtime.

Switching the server is easy. Simply exclude the Tomcat starter and add the dependency you want as shown here with Reactor Netty:

<dependency>
	<groupId>org.springframework.boot.experimental</groupId>
	<artifactId>spring-boot-starter-web-reactive</artifactId>
	<exclusions>
		<exclusion>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
		</exclusion>
	</exclusions>
</dependency>
<dependency>
	<groupId>io.projectreactor.ipc</groupId>
	<artifactId>reactor-netty</artifactId>
</dependency>

An example of the same in Gradle and a switch to RxNetty:

compile('org.springframework.boot.experimental:spring-boot-starter-web-reactive') {
	exclude group: 'org.springframework.boot', module: 'spring-boot-starter-tomcat'
}
compile "io.reactivex:rxnetty-common"
compile "io.reactivex:rxnetty-http"
compile "io.reactivex:rxjava-reactive-streams"

Below are the supported server runtimes. For the exact dependencies check out the sample project build:

• Reactor Netty
• Tomcat
• Jetty
• RxNetty
• Undertow

As described in the "Reactive Web Applications" Spring Framework 5.0 reference documentation, the Web Reactive framework comes in 2 flavors :

• Annotation-based with @Controller and the other annotations supported also with Spring MVC
• Functional, Java 8 lambda style routing and handling

Support of the annotation-based variant works like Spring MVC supports: @Controller beans are taking automatically in account. But we also introduced support for the functional variant. Such support is triggered by RouterFunction beans which can be annotated with any @Component style annotation (@Controller being one of the possible choices if you put your RouterFunction and HandlerFunctionin the same class). You can see an example of such Spring Boot functional web application with this functional-web-playground java-based sample application or this MiXiT Kotlin-based project.

Spring Framework 5 also provides a reactive WebClient. For now the only supported HTTP client is Reactor Netty. Other HTTP clients such as Jetty and RxNetty will be added in the next milestone.

The Spring team has published a few blog posts on the subject:

• Reactive Spring
• Understanding Reactive types
• Notes on Reactive Programming part I, part II and part III

This starter doesn't work with plain @SpringBootTests (i.e. with a WebEnvironment.MOCK, which is the default):

Caused by: java.lang.IllegalArgumentException: Unable to call initializer.
Object of class [org.springframework.boot.context.embedded.ReactiveWebApplicationContext]
must be an instance of interface org.springframework.web.context.ConfigurableWebApplicationContext

Web integration tests @SpringBootTests are working properly, for example @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT).

I've found an issue, I have a question - where should I report it?

• You can report issues in this Github project or on https://jira.spring.io if this is a Spring Framework issue
• You can ask questions in Github issues as well or join the Gitter chat

Will this be available in Spring Boot? When?

Yes! Check out the Spring Boot milestones and especially the dedicated issue.

Is Spring Boot required to run Spring Web Reactive?

It certainly makes things easier, but it's not mandatory. For manual bootstrapping, please [read the reference documentation] (http://docs.spring.io/spring-framework/docs/5.0.0.BUILD-SNAPSHOT/spring-framework-reference/html/web-reactive.html#web-reactive-getting-started-manual).