helidon-io/helidon

Helidon is a set of Java libraries from Oracle for building microservices, which are small, independently deployable server programs that each handle a specific part of an application. It is an alternative to larger Java application servers, designed specifically for building web APIs and backend services. The current version runs on a web server called Helidon Nima, built from scratch to use a Java 21 feature called virtual threads. Virtual threads let the server handle many requests concurrently without the complexity of traditional asynchronous programming. Developers can write code in an ordinary step-by-step blocking style and still get the high-throughput performance usually associated with reactive servers. Earlier versions of Helidon used a reactive model where code had to be written in a callback or promise-based style, which is harder to read and debug. The switch to virtual threads in Helidon 4 simplified the API considerably, though code written for Helidon 3 does require changes to run on the new version. The README links to an upgrade guide covering what needs to be updated. Helidon is distributed as Maven packages under the group ID io.helidon, so there is no separate installer: you reference it in your project build configuration like any other Java dependency. A command-line tool called Helidon CLI is available on macOS, Linux, and Windows to help generate new project starters. Building from source requires JDK 26 and Maven 3.8 or newer. The project is open source under the Apache License 2.0. Documentation and API references are available at helidon.io. Community help is available through Stack Overflow using the helidon tag and through a dedicated Slack channel.