Why spring-webflux application is running on tomcat as default, instead of netty? - spring-webflux

Question

I created a Spring-webflux project using below pom.xml but when I am starting the application, it's starting on Tomcat. Shouldn't it start default on Netty?
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.5.RELEASE</version>
</parent>
<groupId>com.test</groupId>
<artifactId>reactive-rest</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>reactive-rest</name>
<properties>
<java-version>1.8</java-version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-r2dbc</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-rsocket</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-websocket</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-messaging</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-rsocket</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>io.projectreactor</groupId>
<artifactId>reactor-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
</plugin>
</plugins>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>${java-version}</source>
<target>${java-version}</target>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
The main class:
#SpringBootApplication(exclude = {SecurityAutoConfiguration.class, WebMvcAutoConfiguration.class})
public class ReactiveRestApplication {
public static void main(String[] args) {
SpringApplication.run(ReactiveRestApplication.class, args);
}
}
Start logs:
2020-11-09 18:29:26.311 INFO 80838 --- [ restartedMain] o.s.b.d.a.OptionalLiveReloadServer : LiveReload server is running on port 35729
2020-11-09 18:29:26.375 INFO 80838 --- [ restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2020-11-09 18:29:26.390 INFO 80838 --- [ restartedMain] c.o.r.ReactiveRestApplication : Started ReactiveRestApplication in 18.256 seconds (JVM running for 25.2)
I even tried removing tomcat dependency but still the application starts on Tomcat
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</exclusion>
</exclusions>
</dependency>
Even tried setting spring.main.web-application-type: reactive but still tomcat.
Update: I kept only spring-boot-starter-webflux and removed every other dependency. This time also service started on 'Tomcat'

Answer 1

If you look up the different libraries you have included on mvnrepository you can see that spring-boot-starter-websocket
Has a dependency on spring-boot-starter-web which in turn will force default start your app as a springMVC application, and not a webflux application.
My assumption is that websockets are already included in the webflux dependency.