Using Undertow as an Alternative to Tomcat in Spring Boot

In this tutorial the author, a senior architect, introduces Spring Boot’s default embedded Tomcat container and shows how to replace it with the high‑performance Undertow server.

1. Spring Boot’s Tomcat Container

Spring Boot is a popular Java web framework that uses Tomcat as its default embedded servlet container, simplifying project setup and deployment.

2. Setting Up Undertow in Spring Boot

Undertow is a flexible, high‑performance web server written in Java, supporting both blocking and non‑blocking I/O, fully compatible with Servlet 4.0, WebSocket, and designed for embedded use.

High performance under load

Supports Servlet 4.0

Full WebSocket support (JSR‑356)

Embedded – no external container needed

Lightweight, composed of two core JARs

Highly flexible handler chain configuration

To switch to Undertow, modify the Maven dependencies as follows:

<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>

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

After updating the dependencies and restarting the application, the embedded server is now Undertow.

3. Tomcat vs. Undertow Comparison

Both servers are lightweight servlet containers, but Undertow offers superior performance and lower memory consumption under high concurrency. The article includes benchmark images showing QPS and memory usage for each server.

The tests show that Undertow consistently outperforms Tomcat in both throughput and memory usage, especially in high‑concurrency scenarios.

4. Final Remarks

Spring Boot can run either Tomcat or Undertow as its HTTP server. For high‑traffic applications, Undertow provides better performance and lower resource consumption, making it a recommended choice.

After the technical tutorial, the article also contains promotional sections advertising AI tools, a paid community offering ChatGPT accounts, training materials, and other commercial services.