Top 3 Java Micro Framework Projects

Armeria

7 4,664 9.6 Java

Your go-to microservice framework for any situation, from the creator of Netty et al. You can build any type of microservice leveraging your favorite technologies, including gRPC, Thrift, Kotlin, Retrofit, Reactive Streams, Spring Boot and Dropwizard.
Jooby

13 1,658 9.7 Java

The modular web framework for Java and Kotlin

Project mention: Javalin – a simple web framework for Java and Kotlin | news.ycombinator.com | 2024-02-11

One of the good things about it is that using asynchrony is optional. If you don't have to call out anywhere to build the response, processing can all stay in the handler's calling thread. If you do, you can return a future and have the library handle the async for you.
One downside is that it is based on Jetty which isn't considered the most performant backend. A lib with a similar API but based on Netty is Jooby [1] which scores well in the Techempower benchmarks.
[1] - https://jooby.io/
WorkOS

workos.com
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The modern identity platform for B2B SaaS. The APIs are flexible and easy-to-use, supporting authentication, user identity, and complex enterprise features like SSO and SCIM provisioning.
colesico-framework

2 15 6.2 Java

Micro framework for creating server side applications in Java 17+

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020). The latest post mention was on 2024-02-11.