By default, Spring Boot is geared up to use embedded Netty (http://netty.io). Why? Because it's one of the most popular solutions for reactive applications. And when it comes to reactive applications, it's critical that the entire stack be reactive.

However, it's possible to switch to another embedded container. We can experiment with using Apache Tomcat and its asynchronous Servlet 3.1 API. All we have to do is to make some tweaks to the dependency settings in build.gradle, as follows:

    compile('org.springframework.boot:spring-boot-starter-webflux') { 
      exclude group: 'org.springframework.boot', 
      module: 'spring-boot-starter-reactor-netty' 
    } 
    compile('org.springframework.boot:spring-boot-starter-tomcat') 

What's happening in the preceding code? This can be explained as follows:

• spring-boot-starter-webflux excludes spring-boot-starter-reactor-netty, taking it off the classpath
• spring-boot-starter-tomcat is added to the classpath
• Spring Boot's TomcatAutoConfiguration kicks in, and configures the container to work using TomcatReactiveWebServerFactory

It's important to point out that there are these other containers available:

• Jetty
• Undertow

For the rest of this title, we'll stick with Spring Boot's default, Netty.