h2

Helidon SE application that uses the dbclient API with an in-memory H2 database.

Build and run

This example requires a database, see Database Setup.

With JDK21

mvn package
java -jar target/h2.jar

Exercise the application

Basic:

curl -X GET http://localhost:8080/simple-greet
Hello World!

JSON:

curl -X GET http://localhost:8080/greet
{"message":"Hello World!"}

curl -X GET http://localhost:8080/greet/Joe
{"message":"Hello Joe!"}

curl -X PUT -H "Content-Type: application/json" -d '{"greeting" : "Hola"}' http://localhost:8080/greet/greeting

curl -X GET http://localhost:8080/greet/Jose
{"message":"Hola Jose!"}

Database:

# List all Pokémon
curl http://localhost:8080/db/pokemon

# List all Pokémon types
curl http://localhost:8080/db/type

# Get a single Pokémon by id
curl http://localhost:8080/db/pokemon/2

# Get a single Pokémon by name
curl http://localhost:8080/db/pokemon/name/Squirtle

# Add a new Pokémon Rattata
curl -i -X POST -d '{"id":7,"name":"Rattata","idType":1}' http://localhost:8080/db/pokemon

# Rename Pokémon with id 7 to Raticate
curl -i -X PUT -d '{"id":7,"name":"Raticate","idType":2}' http://localhost:8080/db/pokemon

# Delete Pokémon with id 7
curl -i -X DELETE http://localhost:8080/db/pokemon/7

Try metrics

# Prometheus Format
curl -s -X GET http://localhost:8080/observe/metrics
# TYPE base:gc_g1_young_generation_count gauge
. . .

# JSON Format
curl -H 'Accept: application/json' -X GET http://localhost:8080/observe/metrics
{"base":...
. . .

Try health

This example shows the basics of using Helidon SE Health. It uses the set of built-in health checks that Helidon provides plus defines a custom health check.

Note the port number reported by the application.

Probe the health endpoints:

curl -X GET http://localhost:8080/observe/health
curl -X GET http://localhost:8080/observe/health/ready

Building a Native Image

The generation of native binaries requires an installation of GraalVM 22.1.0+.

You can build a native binary using Maven as follows:

mvn -Pnative-image install -DskipTests

The generation of the executable binary may take a few minutes to complete depending on your hardware and operating system. When completed, the executable file will be available under the target directory and be named after the artifact ID you have chosen during the project generation phase.

Database Setup

In the pom.xml and application.yaml we provide configuration needed for h2 database. Start your database before running this example.

Example docker commands to start databases in temporary containers:

H2:

docker run --rm --name h2 -p 9092:9082 -p 8082:8082 nemerosa/h2

For details, see https://www.h2database.com/html/cheatSheet.html

Building the Docker Image

docker build -t h2 .

Running the Docker Image

docker run --rm -p 8080:8080 h2:latest

Exercise the application as described above.

Run the application in Kubernetes

If you don’t have access to a Kubernetes cluster, you can install one on your desktop.

Verify connectivity to cluster

kubectl cluster-info                        # Verify which cluster
kubectl get pods                            # Verify connectivity to cluster

Deploy the application to Kubernetes

kubectl create -f app.yaml                              # Deploy application
kubectl get pods                                        # Wait for quickstart pod to be RUNNING
kubectl get service  h2                     # Get service info
kubectl port-forward service/h2 8081:8080   # Forward service port to 8081

You can now exercise the application as you did before but use the port number 8081.

After you’re done, cleanup.

kubectl delete -f app.yaml

Building a Custom Runtime Image

Build the custom runtime image using the jlink image profile:

mvn package -Pjlink-image

This uses the helidon-maven-plugin to perform the custom image generation. After the build completes it will report some statistics about the build including the reduction in image size.

The target/h2-jri directory is a self contained custom image of your application. It contains your application, its runtime dependencies and the JDK modules it depends on. You can start your application using the provide start script:

./target/h2-jri/bin/start

Class Data Sharing (CDS) Archive Also included in the custom image is a Class Data Sharing (CDS) archive that improves your application’s startup performance and in-memory footprint. You can learn more about Class Data Sharing in the JDK documentation.

The CDS archive increases your image size to get these performance optimizations. It can be of significant size (tens of MB). The size of the CDS archive is reported at the end of the build output.

If you’d rather have a smaller image size (with a slightly increased startup time) you can skip the creation of the CDS archive by executing your build like this:

mvn package -Pjlink-image -Djlink.image.addClassDataSharingArchive=false

For more information on available configuration options see the helidon-maven-plugin documentation.