2. Getting started with Helidon

2.1 Introduction

2.1.1 What you will learn

Here are the key learnings you will get with this hands-on execise:

• Learn how to use the microprofile starter to generate your first Microprofile application, using Helidon as the runtime;
• Explore the basic structure of a Helidon project;
• Learn how to use Helidon CLI;
• Check the experience of the Dev Loop with Helidon CLI.

2.2 Pre requisites

To be able to go through this guided exercise, you will need to have the following components in your dev environment:

• Have finished the steps described in Preparing your environment

2.3 Hands-on practice

2.3.1 Creating a new project

1. Let's create a new project using MP Starter page. Access the page https://start.microprofile.io/.

2. Use the following the data and click on download. You will get a zip file with an automatically generated project for you to get started.

   Method	Description
   groupId	org.a4j
   artifactId	hello-helidon
   MicroProfile Version	3.3
   Build Tool	Maven
   MicroProfile Runtime	Helidon

3. Unzip the file hello-helidon.zip. You should have a project structure like this:

   .
   ├── pom.xml
   ├── readme.md
   └── src
   └── main
   ├── java
   │   └── org
   │       └── a4j
   │           └── hello
   │               └── helidon
   │                   ├── HelloController.java
   │                   └── HellohelidonRestApplication.java
   └── resources
   ├── META-INF
   │   ├── beans.xml
   │   └── microprofile-config.properties
   ├── WEB
   │   └── index.html
   ├── logging.properties
   └── privateKey.pem
   

4. Explore the classes and check what is available out of the box, when we don't select any extra features in the starter page.

2.3.2 Running the project

1. Open the terminal and access the project's folder.

2. Run the following maven command. Maven will download the dependencies described in the project's pom.xml file. It will also create an executable jar we can use to access our application: hello-payara-microbundle.jar.

   mvn clean package
   

3. Now, let's start our first Helidon service. In the terminal, run the following command:

   java -jar target/hello-helidon.jar
   

4. If everything goes well, you should see an output similar to:

    INFO io.helidon.microprofile.server.ServerCdiExtension !thread!: Server started on http://localhost:8080 (and all other host addresses) in 2319 milliseconds (since JVM startup).
    INFO io.helidon.common.HelidonFeatures !thread!: Helidon MP 2.4.1 features: [CDI, Config, Fault Tolerance, Health, JAX-RS, Metrics, Open API, REST Client, Security, Server, Tracing]
   

5. In your browser, access the page http://localhost:8080/data/hello

   What are the classes that are responding to this request?

6. Now change the message that is displayed in this page.

7. Package your application, start it again, and check the changes on the page.

2.4 Using Helidon CLI [Optional]

You can use Helidon CLI for executing tasks like creating new projects and using a feature called "Developer Loop". The Developer Loop allows you to leverage hot reload features while coding your helidon services.

1. Using a terminal, access your project's folder hello-helidon.
2. Run the app using the dev loop with:

   helidon dev
   

3. After the tool finishes downloading the artifacts, you should be able to see something like:

   | downloading artifacts
   | building
   | build completed (1.9 seconds)
   | hello-helidon starting
   
   ...
   
   2022.05.27 22:59:32 INFO io.helidon.common.HelidonFeatures !thread!: Helidon MP 2.4.1 features: [CDI, Config, Fault Tolerance, Health, JAX-RS, Metrics, Open API, REST Client, Security, Server, Tracing]
   

   Alert

   Sometimes the dev loop might not work on the first initialization of helidon dev. To avoid issues, you can stop the service with ctrl+c (or cmd+c) and start it again with helidon dev.

4. Open the service in your browser: http://localhost:8080/data/hello

5. On your IDE, open the class org.a4j.hello.helidon.HelloController

6. Change the endpoint path to devloop and the string returned by the method sayHello to "Hello Dev Loop!"
7. Back in your browser, check your changes reflected at http://localhost:8080/data/devloop

2.5 Additional information

When you are you GraalVM, you can compile your helidon services using Ahead of Time compilation. AoT is a strategy to have the compilation processing during build time, allowing you to create native executable files with fast startup time.

For more information check the Helidon docs for Helidon SE GraalVM native image.