Comparing Tomcat and Undertow in SpringBoot: Performance and Memory Usage

Introduction

In SpringBoot the default embedded servlet container is Tomcat, which is widely used for Java web applications.

SpringBoot also supports the Undertow container, which offers better performance and lower memory usage; this article shows how to switch to Undertow.

SpringBoot’s Tomcat Container

SpringBoot is a popular Java web framework that simplifies development by eliminating XML configuration and providing an embedded Tomcat server to run web services.

Configuring Undertow in SpringBoot

To replace Tomcat with Undertow, add the Undertow starter dependency to the project. After rebuilding, the application starts with Undertow as the embedded server.

Comparison of Tomcat and Undertow

Tomcat is an Apache‑licensed lightweight servlet container that also includes an HTTP server; it is free and widely adopted.

Undertow, developed by Red Hat, is a fully Java‑based, flexible, high‑performance web server supporting both blocking and non‑blocking I/O, servlet, and WebSocket.

Benchmark Results

Performance tests on identical hardware measured QPS and memory usage. The Tomcat results are shown in the first chart, Undertow results in the second.

Undertow QPS chart:

Memory usage comparison:

The tests indicate that Undertow delivers higher throughput and uses less memory than Tomcat under high concurrency.

Conclusion

Both Tomcat and Undertow can serve HTTP in SpringBoot, but Undertow outperforms Tomcat in high‑concurrency scenarios, making it the preferred choice for performance‑critical services.