Spring Boot Undertow

last modified July 16, 2023

Spring Boot Undertow tutorial shows how to use Undertow server in a Spring Boot application.

Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.

Undertow

Undertow is a flexible performant web server which provides both blocking and non-blocking API’s. It comes from the JBoss project.

Spring Boot Undertow example

By default, Spring Boot uses a Tomcat embedded web server. The following example shows how to use Undertow.

build.gradle … src ├───main │ ├───java │ │ └───com │ │ └───zetcode │ │ │ Application.java │ │ ├───config │ │ │ AppConfig.java │ │ └───controller │ │ MyController.java │ └───resources │ application.properties └───test └───java

This is the project structure.

build.gradle

plugins { id ‘org.springframework.boot’ version ‘3.1.1’ id ‘io.spring.dependency-management’ version ‘1.1.0’ id ‘java’ }

group = ‘com.zetcode’ version = ‘0.0.1-SNAPSHOT’ sourceCompatibility = ‘17’

repositories { mavenCentral() }

dependencies { implementation(‘org.springframework.boot:spring-boot-starter-web’) { exclude group: ‘org.springframework.boot’, module: ‘spring-boot-starter-tomcat’ }

implementation 'org.springframework.boot:spring-boot-starter-undertow'

}

This is the Gradle build file. We explicitly exclude the Tomcat server dependency and include the Undertow dependency.

resources/application.properties

spring.main.banner-mode=off

In the application.properties file we have various configuration settings of a Spring Boot application. With the spring.main.banner-mode property we turn off the Spring banner.

com/zetcode/controller/MyController.java

package com.zetcode.controller;

import org.springframework.http.MediaType; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController;

@RestController public class MyController {

@GetMapping(value="/", produces = MediaType.TEXT_PLAIN_VALUE)
public String home() {

    return "Home page";
}

}

The home page returns a simple text message.

com/zetcode/config/AppConfig.java

package com.zetcode.config;

import org.springframework.boot.web.embedded.undertow.UndertowBuilderCustomizer; import org.springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration;

@Configuration public class AppConfig {

@Bean
public UndertowServletWebServerFactory embeddedServletContainerFactory() {
    UndertowServletWebServerFactory factory =
            new UndertowServletWebServerFactory();

    factory.addBuilderCustomizers((UndertowBuilderCustomizer)
            builder -> builder.addHttpListener(8081, "0.0.0.0"));

    return factory;
}

}

We set up the Undertow server. The server will listen on port 8081.

–>

com/zetcode/Application.java

package com.zetcode;

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

@SpringBootApplication public class Application {

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

}

The Application is the entry point which sets up Spring Boot application.

$ ./gradlew bootRun

We run the application and navigate to localhost:8080.

… … io.undertow : starting server: Undertow - 2.3.7.Final … org.xnio : XNIO version 3.8.8.Final … org.xnio.nio : XNIO NIO Implementation Version 3.8.8.Final … org.jboss.threads : JBoss Threads version 3.5.0.Final … o.s.b.w.e.undertow.UndertowWebServer : Undertow started on port(s) 8080 (http)

In the console we can see the Undertow server starting.

In this article we have shown how use Undertow server in a Spring Boot application.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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