Configure an Explicit External Server in Spring Boot

To configure an explicit server, such as Jetty, in a Spring Boot application, you need to include the appropriate Spring Boot starter for Jetty and exclude the default Tomcat starter. This setup allows Spring Boot to use Jetty as the embedded server instead of Tomcat. Here’s a step-by-step guide on how to achieve this, including the necessary code.

Step 1: Modify the pom.xml File

First, you need to adjust your Maven pom.xml file to include the Jetty starter dependency and exclude the default Tomcat starter. This tells Maven to pull in Jetty libraries during the build process.

<dependencies>
    <!-- Exclude the default Tomcat dependency -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <exclusions>
            <exclusion>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-tomcat</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

    <!-- Add Jetty starter dependency -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jetty</artifactId>
    </dependency>
</dependencies>

Step 2: Spring Boot Application Configuration

In your Spring Boot application, no additional configuration is required specifically for Jetty if you are using the defaults. Spring Boot auto-configures Jetty with sensible defaults. However, if you need to customize Jetty settings, you can do so in your application.properties or application.yml file.

Here’s an example of how you might configure common Jetty server properties in application.properties:

server.port=8080
server.jetty.accesslog.enabled=true
server.jetty.accesslog.filename=access.log
server.jetty.accesslog.format=%{client}a - %u %{server}t "%r" %s %O
server.jetty.max-http-post-size=2048

Step 3: Main Application Class

Your main application class remains standard as per any Spring Boot application. Here’s a simple example:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class JettyApplication {

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

Step 4: Running Your Application

Run your application using your IDE or through the command line by executing mvn spring-boot:run. Spring Boot will automatically start using Jetty as the embedded server.

Additional Customizations

If you need more advanced configurations, such as setting up SSL or configuring session management in Jetty, you can define a JettyServerCustomizer bean in your configuration:

import org.eclipse.jetty.server.Server;
import org.springframework.boot.web.embedded.jetty.JettyServerCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class JettyConfig {

    @Bean
    public JettyServerCustomizer jettyServerCustomizer() {
        return new JettyServerCustomizer() {
            @Override
            public void customize(Server server) {
                // Customize the server configuration
            }
        };
    }
}

This setup allows you to directly manipulate the Jetty server instance, giving you access to the full breadth of Jetty’s server configuration options.

Conclusion

Configuring Jetty as the server in a Spring Boot application involves excluding the default Tomcat starter and including the Jetty starter dependency. Spring Boot’s auto-configuration takes care of the rest, but you can always customize the server settings via properties or programmatically through JettyServerCustomizer. This flexibility makes it straightforward to integrate Jetty into your Spring Boot projects for scenarios where specific