Spring Boot WebFlux NettyServerCustomizer does not work - spring-mvc

Question

I have very simple application, I read I can use NettyServerCustomizer to customize NettyServer. But it does not work, implementation of the NettyServerCustomizer interface is not being called.
Project is generated by Spring Initializr
Code of application:
#SpringBootApplication
#RestController
#RequestMapping("/test")
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
#GetMapping
public Mono<String> test() {
return Mono.just("test");
}
#Bean
public NettyServerCustomizer nettyCustomizer() {
return builder -> builder.port(9909);
}
}
pom
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.1.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>io.projectreactor</groupId>
<artifactId>reactor-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

Answer 1

Defining a bean of type NettyServerCustomizer doesn't have any effect by itself, you can get the desired result with WebServerFactoryCustomizer
#Bean
public WebServerFactoryCustomizer getWebServerFactoryCustomizer() {
WebServerFactoryCustomizer<ConfigurableReactiveWebServerFactory> customizer = factory -> factory.setPort(9909);
return customizer;
}
Also note that the port is also read from the Environment using the property server.port, which I think the cleanest way besides it has a great deal of flexibility regarding the source of the property value.
If you are wondering why NettyServerCustomizer doesn't work, a bit of digging in the code reveals that this class is not injected into NettyReactiveWebServerFactory in any way.