Our sample application uses Spring Boot. Spring WebFlux runs on a Reactor Netty server within Spring Boot by default. Our Spring Boot class is very basic and is as follows:

@SpringBootApplication
public class Run {
  public static void main(String[] args) {
      SpringApplication.run(Run.class, args);
  }
}

You can run the application on any other server, apart from Spring Boot, and it is quite easy to achieve. We have a separate project named spring-boot-tomcat-webflux that runs on Spring Boot, but rather than running on Reactor Netty, it runs on a Tomcat server.

No change is required in any part of the code, apart from pom.xml:

<!--Spring Framework and Spring Boot-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-webflux</artifactId>
  <exclusions>
      <exclusion>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-reactor-netty</artifactId>
      </exclusion>
  </exclusions>
</dependency>
<!--Explicit Tomcat dependency-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-tomcat</artifactId>
</dependency>

From the spring-boot-starter-webflux artifact, exclude Reactor Netty. Thereafter, explicitly add the Tomcat dependency, spring-boot-starter-tomcat. The rest of the pom.xml is kept intact. For other server runtimes, such as Undertow, Jetty, and so on, the approach is similar to the one detailed here.