What Is Undertow Web Server?


Heather Bennett

What Is Undertow Web Server?

Undertow is a lightweight, high-performance web server written in Java. It is designed to be flexible, scalable, and efficient, making it an excellent choice for building modern web applications.

In this tutorial, we will explore the features and advantages of Undertow and learn how to get started with it.

Advantages of Undertow Web Server

Undertow offers several key advantages over other web servers:

  • Lightweight: Undertow has a small memory footprint and minimal overhead, making it suitable for resource-constrained environments.
  • High Performance: With its non-blocking architecture, Undertow can handle a large number of concurrent connections efficiently.
  • Flexibility: Undertow provides a modular architecture that allows developers to choose and configure only the components they need for their application.
  • Embeddable: It is easy to embed Undertow into existing applications or frameworks to provide HTTP server capabilities.
  • WebSocket Support: Undertow includes built-in support for WebSocket communication, enabling real-time bidirectional communication between clients and servers.

Getting Started with Undertow Web Server

To start using Undertow in your Java project, follow these steps:

Add Maven Dependency

To include Undertow in your project using Maven, add the following dependency to your pom.xml:


Create a Simple Undertow Server

Here’s an example of a simple Undertow server:

import io.undertow.Undertow;
import io.server.HttpHandler;
import io.HttpServerExchange;

public class SimpleServer {
    public static void main(String[] args) {
        Undertow server = Undertow.builder()
                .addHttpListener(8080, "localhost")
                .setHandler(new HttpHandler() {
                    public void handleRequest(HttpServerExchange exchange) throws Exception {
                        exchange.getResponseSender().send("Hello, Undertow!");

In this example, we create an instance of the Undertow server and configure it to listen on port 8080 for incoming HTTP requests. We set the handler to a simple implementation that sends the response “Hello, Undertow!”

back to the client.

Run the Server

Compile and run the SimpleServer class. You should see the server start up and listen for incoming connections on port 8080.

$ javac SimpleServer.java
$ java SimpleServer

Now you can open your web browser and navigate to http://localhost:8080. You should see the message “Hello, Undertow!”

displayed in your browser.


Undertow is a powerful and lightweight web server that offers excellent performance and flexibility. It is an ideal choice for building modern web applications that require high concurrency and low resource usage.

By following the steps outlined in this tutorial, you can easily get started with Undertow and take advantage of its many features.

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