Configure the Web Server

Generally, you should first consider using one of the many available configuration keys and customize your web server by adding new entries in your application.properties or application.yml file. See “Discover Built-in Options for External Properties”). The server.* namespace is quite useful here, and it includes namespaces like server.tomcat.*, server.jetty.* and others, for server-specific features. See the list of Common Application Properties.

The previous sections covered already many common use cases, such as compression, SSL or HTTP/2. However, if a configuration key does not exist for your use case, you should then look at WebServerFactoryCustomizer. You can declare such a component and get access to the server factory relevant to your choice: you should select the variant for the chosen Server (Tomcat, Jetty, Reactor Netty, Undertow) and the chosen web stack (servlet or reactive).

The example below is for Tomcat with the spring-boot-starter-web (servlet stack):

Java
Kotlin

import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.stereotype.Component;

@Component
public class MyTomcatWebServerCustomizer implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

	@Override
	public void customize(TomcatServletWebServerFactory factory) {
		// customize the factory here
	}

}

import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory
import org.springframework.boot.web.server.WebServerFactoryCustomizer
import org.springframework.stereotype.Component

@Component
class MyTomcatWebServerCustomizer : WebServerFactoryCustomizer<TomcatServletWebServerFactory?> {

	override fun customize(factory: TomcatServletWebServerFactory?) {
		// customize the factory here
	}

}

Spring Boot uses that infrastructure internally to auto-configure the server. Auto-configured WebServerFactoryCustomizer beans have an order of 0 and will be processed before any user-defined customizers, unless it has an explicit order that states otherwise.

Once you have got access to a WebServerFactory using the customizer, you can use it to configure specific parts, like connectors, server resources, or the server itself - all using server-specific APIs.

In addition Spring Boot provides:

Server Servlet stack Reactive stack

Server	Servlet stack	Reactive stack
Tomcat	`TomcatServletWebServerFactory`	`TomcatReactiveWebServerFactory`
Jetty	`JettyServletWebServerFactory`	`JettyReactiveWebServerFactory`
Undertow	`UndertowServletWebServerFactory`	`UndertowReactiveWebServerFactory`
Reactor	N/A	`NettyReactiveWebServerFactory`

Tomcat

TomcatServletWebServerFactory

TomcatReactiveWebServerFactory

Jetty

JettyServletWebServerFactory

JettyReactiveWebServerFactory

Undertow

UndertowServletWebServerFactory

UndertowReactiveWebServerFactory

Reactor

N/A

NettyReactiveWebServerFactory

As a last resort, you can also declare your own WebServerFactory bean, which will override the one provided by Spring Boot. When you do so, auto-configured customizers are still applied on your custom factory, so use that option carefully.