Replacing Tomcat with Undertow in Spring Boot: Configuration and Performance Comparison

Introduction

Spring Boot uses Tomcat as its default embedded servlet container, but it also supports Undertow, which offers better performance and lower memory consumption. This article explains how to switch from Tomcat to Undertow.

Tomcat in Spring Boot

Spring Boot is a popular Java web framework that simplifies creating web services. Tomcat is the default embedded container, providing servlet and JSP support.

Configuring Undertow in Spring Boot

To replace Tomcat with Undertow, simply add the Undertow starter dependency to the project (e.g., in Maven or Gradle). After adding the dependency and rebuilding, the application starts with Undertow as the embedded server.

Tomcat vs. Undertow Comparison

Tomcat is a lightweight servlet container that includes an HTTP server, while Undertow is a Red Hat open‑source, Java‑based, high‑performance web server supporting both blocking and non‑blocking I/O, servlet, and WebSocket.

Benchmark Results

Performance tests on identical hardware show that Undertow achieves higher QPS and uses less memory than Tomcat under the same request load.

QPS Comparison

Images illustrate that Undertow processes more requests per second than Tomcat.

Memory Usage Comparison

Images demonstrate that Undertow consumes less memory than Tomcat.

Conclusion

For high‑concurrency business systems, Undertow outperforms Tomcat in both throughput and memory efficiency, making it the preferred choice when replacing Tomcat in Spring Boot applications.