Hello World - Java (Quarkus)

A simple JAX-RS REST API application that is written in Java and uses Quarkus.

This samples uses Docker to build locally. The app reads in a TARGET env variable and then prints “Hello World: ${TARGET}!”. If a value for TARGET is not specified, the “NOT SPECIFIED” default value is used.

Before you begin

You must meet the following requirements to run this sample:

Getting the code

You can either clone a working copy of the sample code from the repository, or following the steps in the Recreating the sample code to walk through the steps of updating all the files.

Cloning the sample code

Use this method to clone and then immediate run the sample. To clone the sample code, run the following commands:

git clone -b "release-0.23" https://github.com/knative/docs.git knative/docs
cd knative/docs/community/samples/serving/helloworld-java-quarkus

You are now ready to run the sample locally.

Recreating the sample code

Use the following steps to obtain an incomplete copy of the sample code for which you update and create the necessary build and configuration files:

  1. From the console, create a new empty web project using the Maven archetype commands:

    mvn io.quarkus:quarkus-maven-plugin:0.13.3:create \
     -DprojectGroupId=com.redhat.developer.demos \
     -DprojectArtifactId=helloworld-java-quarkus \
     -DclassName="com.redhat.developer.demos.GreetingResource" \
  2. Update the GreetingResource class in src/main/java/com/redhat/developer/demos/GreetingResource.java to handle the “/” mapping and also add a @ConfigProperty field to provide the TARGET environment variable:

    package com.redhat.developer.demos;
    import javax.ws.rs.GET;
    import javax.ws.rs.Path;
    import javax.ws.rs.Produces;
    import javax.ws.rs.core.MediaType;
    import org.eclipse.microprofile.config.inject.ConfigProperty;
    public class GreeterResource {
      @ConfigProperty(name = "TARGET", defaultValue="World")
      String target;
      public String greet() {
        return "Hello " + target + "!";
  3. Update src/main/resources/application.properties to configuration the application to default to port 8080, but allow the port to be overridden by the PORT environmental variable:

    # Configuration file
    # key = value
  4. Update src/test/java/com/redhat/developer/demos/GreetingResourceTest.java test to reflect the change:

    package com.redhat.developer.demos;
    import io.quarkus.test.junit.QuarkusTest;
    import org.junit.jupiter.api.Test;
    import static io.restassured.RestAssured.given;
    import static org.hamcrest.CoreMatchers.is;
    public class GreetingResourceTest {
      public void testHelloEndpoint() {
              .body(is("Hello World!"));
  5. Remove src/main/resources/META-INF/resources/index.html file since it’s unncessary for this example.

    rm src/main/resources/META-INF/resources/index.html
  6. Remove .dockerignore file since it’s unncessary for this example.

    rm .dockerignore
  7. In your project directory, create a file named Dockerfile and copy the code block below into it.

    FROM quay.io/rhdevelopers/quarkus-java-builder:graal-1.0.0-rc15 as builder
    COPY . /project
    WORKDIR /project
    # uncomment this to set the MAVEN_MIRROR_URL of your choice, to make faster builds
    # ARG MAVEN_MIRROR_URL=<your-maven-mirror-url>
    # e.g.
    RUN /usr/local/bin/entrypoint-run.sh mvn -DskipTests clean package
    FROM fabric8/java-jboss-openjdk8-jdk:1.5.4
    USER jboss
    ENV JAVA_APP_DIR=/deployments
    COPY --from=builder /project/target/lib/* /deployments/lib/
    COPY --from=builder /project/target/*-runner.jar /deployments/app.jar
    ENTRYPOINT [ "/deployments/run-java.sh" ]

    If you want to build Quarkus native image, then copy the following code block in to file called Dockerfile.native

    FROM quay.io/rhdevelopers/quarkus-java-builder:graal-1.0.0-rc15 as builder
    COPY . /project
    # uncomment this to set the MAVEN_MIRROR_URL of your choice, to make faster builds
    # ARG MAVEN_MIRROR_URL=<your-maven-mirror-url>
    # e.g.
    RUN /usr/local/bin/entrypoint-run.sh mvn -DskipTests clean package -Pnative
    FROM registry.fedoraproject.org/fedora-minimal
    COPY --from=builder /project/target/helloworld-java-quarkus-runner /app
    ENTRYPOINT [ "/app" ]
  8. Create a new file, service.yaml and copy the following service definition into the file. Make sure to replace {username} with your Docker Hub username.

    apiVersion: serving.knative.dev/v1
    kind: Service
      name: helloworld-java-quarkus
            - image: docker.io/{username}/helloworld-java-quarkus
                - name: TARGET
                  value: "Quarkus Sample v1"

Locally testing your sample

  1. Run the application locally:

    ./mvnw compile quarkus:dev

    Go to http://localhost:8080/ to see your Hello World! message.

Building and deploying the sample

Once you have recreated the sample code files (or used the files in the sample folder) you’re ready to build and deploy the sample app.

  1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

    # Build the container on your local machine
    docker build -t {username}/helloworld-java-quarkus .
    # (OR)
    # Build the container on your local machine - Quarkus native mode
    docker build -t {username}/helloworld-java-quarkus -f Dockerfile.native .
    # Push the container to docker registry
    docker push {username}/helloworld-java-quarkus
  2. After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in service.yaml matches the container you built in the previous step. Apply the configuration using kubectl:

    kubectl apply --filename service.yaml
  3. Now that your service is created, Knative will perform the following steps:

    • Create a new immutable revision for this version of the app.
    • Network programming to create a route, ingress, service, and load balancer for your app.
    • Automatically scale your pods up and down (including to zero active pods).
  4. To find the URL for your service, use

    kubectl get ksvc helloworld-java-quarkus
    NAME                     URL
    helloworld-java-quarkus  http://helloworld-java-quarkus.default.
  5. Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.

    curl http://helloworld-java-quarkus.default.
    Namaste Knative World!

Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

kubectl delete --filename service.yaml