# Helidon — Java Microservices Framework by Oracle

> A set of Java libraries for writing microservices that run on a fast Helidon WebServer underpinning, with support for MicroProfile and a reactive programming model.

## Install

Save as a script file and run:

# Helidon — Java Microservices Framework by Oracle

## Quick Use
```bash
# Generate a Helidon MP project using the CLI
curl -O https://helidon.io/cli/latest/linux/helidon
chmod +x helidon
./helidon init --flavor MP --groupid com.example --artifactid myapp
cd myapp
mvn package
java -jar target/myapp.jar
# Server starts on http://localhost:8080
```
```java
// JAX-RS resource in Helidon MP
@Path("/greet")
public class GreetResource {
    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public JsonObject getGreeting() {
        return Json.createObjectBuilder()
            .add("message", "Hello from Helidon!")
            .build();
    }
}
```

## Introduction
Helidon is a collection of Java libraries developed by Oracle for building microservices. It offers two programming models: Helidon MP (MicroProfile) for developers who prefer annotation-driven JAX-RS style, and Helidon SE for those who want a lightweight functional/reactive approach without dependency injection frameworks.

## What Helidon Does
- Provides a fast embedded web server based on virtual threads (Loom) in Helidon 4.x
- Implements the Eclipse MicroProfile specification including Config, Health, Metrics, and OpenAPI
- Offers a functional reactive API (Helidon SE) for building services without annotations or CDI
- Integrates with GraalVM Native Image for ahead-of-time compilation to reduce startup time and memory
- Supports built-in service mesh features like tracing (OpenTracing/OpenTelemetry), fault tolerance, and JWT authentication

## Architecture Overview
Helidon 4.x is built on virtual threads (Project Loom), replacing the earlier reactive Netty-based server. Helidon MP layers MicroProfile APIs (CDI, JAX-RS, JSON-P/JSON-B) on top of the core web server, while Helidon SE exposes the same server through a functional routing API without a CDI container. Both flavors share the same underlying HTTP engine, configuration system, and security framework, so features like health checks, metrics endpoints, and tracing work identically regardless of programming model.

## Self-Hosting & Configuration
- Requires JDK 21 or later for virtual thread support in Helidon 4.x
- Use Maven or Gradle with the Helidon BOM (Bill of Materials) for dependency management
- Application configuration is loaded from application.yaml or microprofile-config.properties with environment variable overrides
- Build native executables with GraalVM using the native-image Maven plugin included in Helidon archetypes
- Deploy as a standalone JAR, a Docker container, or on Kubernetes with the provided Dockerfile templates

## Key Features
- Virtual-thread-based server that handles high concurrency without reactive complexity
- Dual programming models (MP and SE) sharing the same runtime and configuration system
- Full MicroProfile compliance for portability across compliant implementations
- GraalVM Native Image support for sub-second startup times
- Built-in observability with health checks, Prometheus-compatible metrics, and distributed tracing

## Comparison with Similar Tools
- **Quarkus** — Red Hat's Java framework with hot reload and native compilation; larger ecosystem and community
- **Micronaut** — compile-time DI framework; similar startup performance but uses annotation processing instead of virtual threads
- **Spring Boot** — dominant Java framework; more libraries and integrations but heavier baseline footprint
- **Vert.x** — reactive toolkit by Eclipse; event-loop model vs. Helidon's virtual-thread approach

## FAQ
**Q: What is the difference between Helidon SE and Helidon MP?**
A: Helidon SE is a functional API with no dependency injection container, suited for developers who want full control. Helidon MP implements Eclipse MicroProfile with CDI and JAX-RS annotations, suited for those familiar with Jakarta EE patterns.

**Q: Does Helidon support GraalVM native images?**
A: Yes. Both Helidon SE and MP support GraalVM Native Image compilation. The Helidon CLI and Maven archetypes include native-image profiles out of the box.

**Q: How does Helidon 4.x differ from earlier versions?**
A: Helidon 4.x replaced the Netty-based reactive server with a virtual-thread server (Project Loom), simplifying the programming model by allowing blocking-style code that scales like reactive code.

**Q: Can Helidon run on Kubernetes?**
A: Yes. Helidon projects generated by the CLI include Dockerfiles and Kubernetes YAML manifests. Health and readiness endpoints are enabled by default for probe configuration.

## Sources
- https://github.com/helidon-io/helidon
- https://helidon.io/docs/v4/about/doc_overview

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Author: Script Depot