Introduction

Helidon is a Java framework for building cloud-native applications. It provides APIs and runtime services for creating standalone applications that are easy to develop, deploy, observe, and scale.

Helidon SE is the foundational set of Helidon APIs. Applications run as standalone JVM processes, are powered by the Helidon WebServer, and give you a direct programming model for defining routes, services, configuration, security, observability, and other application behavior.

Helidon 4 uses Java 21 virtual threads throughout the WebServer, so applications can use a simple blocking style without tying up platform threads for each request.

Strengths

• Full control over application structure and behavior.

• Transparent programming model with explicit APIs.

• High-concurrency services that benefit from virtual threads.

• Small runtime footprint.

• Few third-party dependencies.

• Lightweight HTTP services and microservices.

First Look

A Helidon SE application can start an HTTP server and define a route directly in Java:

WebServer.builder()
    .addRouting(HttpRouting.builder()
        .get("/greet", (req, res)
            -> res.send("Hello World!")))
    .build()
    .start();