[rjst01]

A big advantage that Javalin and some of the other micro-frameworks have over Spring Boot have is that by picking Spring boot, you are also implicitly picking Spring's custom Java classloader and packaging, and Maven or Gradle as a build tool.

The tooling for building Spring Boot apps from other build systems like Bazel has problems, and while you can forego it and build your Spring Boot apps with Bazel's java_binary targets, you really don't want to.

Javalin by contrast is a plain boring Java dependency and you can pull it into any Java app with ease.

I do miss the better support for OpenAPI in Spring Boot though - Javalin's support is still missing a lot of functionality, but it is being very actively developed.