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

Hello, I'm Lei.

Spring Boot's Default Tomcat Container

Spring Boot is currently the most popular Java web framework, allowing developers to create a complete web service within minutes without cumbersome XML configuration. By default, it embeds the Tomcat servlet container to run web applications.

Configuring Undertow in Spring Boot

Besides Tomcat, Spring Boot also supports the Undertow container. To switch, you only need to add the Undertow dependency to your project, as shown in the accompanying diagram.

After adding the dependency and rebuilding, the application starts with Undertow instead of Tomcat.

Why Replace Tomcat with Undertow?

Undertow, an open‑source product from Red Hat, is written entirely in Java, supports both blocking and non‑blocking I/O, and can be embedded directly into Java projects. It fully supports Servlet and WebSocket APIs and demonstrates excellent performance under high concurrency.

Tomcat vs. Undertow: Advantages Comparison

Tomcat, an Apache‑funded lightweight servlet container, includes an HTTP server and offers management tools, but it is generally less efficient for high‑throughput scenarios.

Undertow is a flexible, high‑performance web server that excels in both QPS and memory usage, especially when handling many simultaneous connections.

QPS Test Results

Tomcat

Undertow

Memory Usage Comparison

Tomcat

Undertow

Benchmark results show that under identical hardware, Undertow delivers higher QPS and lower memory consumption than Tomcat, making it the optimal choice for high‑concurrency business systems.

Conclusion

Spring Boot allows you to use either Tomcat or Undertow as the HTTP server. For high‑traffic applications, Undertow provides better performance and resource efficiency, so switching to Undertow can significantly improve system throughput.