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Helidon: Java Libraries for Microservices

Project Helidon is a set of Java Libraries for writing microservices. Helidon supports two programming models:

In either case your application is a Java SE program running on the new Helidon Níma WebServer that has been written from the ground up to use Java 21 Virtual Threads. With Helidon 4 you get the high throughput of a reactive server with the simplicity of thread-per-request style programming.

The Helidon SE API in Helidon 4 has changed significantly from Helidon 3. The use of virtual threads has enabled these APIs to change from asynchronous to blocking. This results in much simpler code that is easier to write, maintain, debug and understand. Earlier Helidon SE code will require modification to run on these new APIs. For more information see the Helidon SE Upgrade Guide.

Helidon 4 supports MicroProfile 6. This means your existing Helidon MP 3.x applications will run on Helidon 4 with only minor modifications. And since Helidon’s MicroProfile server is based on the new Níma WebServer you get all the benefits of running on virtual threads. For more information see the Helidon MP Upgrade Guide.

New to Helidon? Then jump in and get started.

Java 21 is required to use Helidon 4.


Helidon is available under Apache License 2.0.


Latest documentation and javadocs are available at

Helidon White Paper is available here.

Get Started

See Getting Started at

Downloads / Accessing Binaries

There are no Helidon downloads. Just use our Maven releases (GroupID io.helidon). See Getting Started at

Helidon CLI


curl -O
chmod +x ./helidon
sudo mv ./helidon /usr/local/bin/


curl -O
chmod +x ./helidon
sudo mv ./helidon /usr/local/bin/


PowerShell -Command Invoke-WebRequest -Uri "" -OutFile "C:\Windows\system32\helidon.exe"

See this document for more info.


You need JDK 21 to build Helidon 4.

You also need Maven. We recommend 3.8.0 or newer.

Full build

$ mvn install


# cd to the component you want to check
$ mvn validate  -Pcheckstyle


# cd to the component you want to check
$ mvn validate  -Pcopyright


# cd to the component you want to check
$ mvn verify  -Pspotbugs


# At the root of the project
$ mvn site

Build Scripts

Build scripts are located in etc/scripts. These are primarily used by our pipeline, but a couple are handy to use on your desktop to verify your changes.

  • Run a full copyright check
  • Run a full style check

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