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

Introduction

In Spring Boot the default embedded container is Tomcat, but Undertow can be used as a replacement offering better performance and lower memory usage. This article explains how to switch to Undertow and compares the two containers.

Tomcat Container in Spring Boot

Spring Boot is a popular Java web framework that eliminates heavy XML configuration and allows developers to create a complete web service within minutes. Tomcat is the default embedded servlet container used by Spring Boot.

Configuring Undertow in Spring Boot

To replace Tomcat with Undertow, simply add the Undertow starter dependency to the project. After the dependency is added and the application is started, the embedded container switches to Undertow.

Comparison of Tomcat and Undertow

Tomcat is a lightweight servlet container from the Apache foundation that also includes an HTTP server. Undertow, developed by Red Hat, is a flexible high‑performance web server written in Java, supporting both blocking and non‑blocking I/O, servlet, and WebSocket.

QPS Test Results

Undertow

Memory usage comparison

Tomcat

Undertow

Benchmark results show that Undertow outperforms Tomcat in both throughput and memory consumption under high‑concurrency conditions, making it the preferred choice for high‑traffic systems.

Conclusion

Both Tomcat and Undertow can serve as the HTTP engine in Spring Boot, but Undertow delivers superior performance and lower memory usage in high‑concurrency scenarios, so it is recommended for such workloads.