---
title: "Hello World - Spring Boot Java"
linkTitle: "Java (Spring)"
weight: 1
type: "docs"
---

This guide describes the steps required to create the `helloworld-java-spring` sample app and deploy it to your cluster.

The sample app reads a `TARGET` environment variable, and prints `Hello ${TARGET}!`. If `TARGET` is not specified, `World` is used as the default value.

You can also download a working copy of the sample, by running the following commands:

```shell
git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-java-spring
```

## Prerequisites

- A Kubernetes cluster with Knative installed and DNS configured. Follow the
  [installation instructions](../../../../install/README.md).
- [Docker](https://www.docker.com) installed and running on your local machine,
  and a Docker Hub account configured.
- (optional) The Knative CLI client [kn](https://github.com/knative/client/releases) can be used to simplify the deployment. Alternatively, you can use `kubectl`, and apply resource files directly.

## Building the sample app

1. From the console, create a new, empty web project by using the curl and unzip
   commands:

   ```shell
   curl https://start.spring.io/starter.zip \
       -d dependencies=web \
       -d name=helloworld \
       -d artifactId=helloworld \
       -o helloworld.zip
   unzip helloworld.zip
   ```

   If you don't have `curl` installed, you can accomplish the same by visiting the
   [Spring Initializr](https://start.spring.io/) page. Specify Artifact as
   `helloworld` and add the `Web` dependency. Then click `Generate Project`,
   download and unzip the sample archive.

1. Update the `SpringBootApplication` class in
   `src/main/java/com/example/helloworld/HelloworldApplication.java` by adding a
   `@RestController` to handle the "/" mapping and also add a `@Value` field to
   provide the `TARGET` environment variable:

   ```java
   package com.example.helloworld;

   import org.springframework.beans.factory.annotation.Value;
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   import org.springframework.web.bind.annotation.GetMapping;
   import org.springframework.web.bind.annotation.RestController;

   @SpringBootApplication
   public class HelloworldApplication {

     @Value("${TARGET:World}")
     String target;

     @RestController
     class HelloworldController {
       @GetMapping("/")
       String hello() {
         return "Hello " + target + "!";
       }
     }

     public static void main(String[] args) {
       SpringApplication.run(HelloworldApplication.class, args);
     }
   }
   ```

1. Run the application locally:

   ```shell
   ./mvnw package && java -jar target/helloworld-0.0.1-SNAPSHOT.jar
   ```

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

1. In your project directory, create a file named `Dockerfile` and copy the code block below into it:

   ```docker
   # Use the official maven/Java 8 image to create a build artifact.
   # https://hub.docker.com/_/maven
   FROM maven:3.5-jdk-8-alpine as builder

   # Copy local code to the container image.
   WORKDIR /app
   COPY pom.xml .
   COPY src ./src

   # Build a release artifact.
   RUN mvn package -DskipTests

   # Use AdoptOpenJDK for base image.
   # It's important to use OpenJDK 8u191 or above that has container support enabled.
   # https://hub.docker.com/r/adoptopenjdk/openjdk8
   # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
   FROM adoptopenjdk/openjdk8:jdk8u202-b08-alpine-slim

   # Copy the jar to the production image from the builder stage.
   COPY --from=builder /app/target/helloworld-*.jar /helloworld.jar

   # Run the web service on container startup.
   CMD ["java", "-Djava.security.egd=file:/dev/./urandom", "-jar", "/helloworld.jar"]
   ```
For detailed instructions on dockerizing a Spring Boot app, see [Spring Boot with Docker](https://spring.io/guides/gs/spring-boot-docker/).

For additional information on multi-stage docker builds for Java see [Creating Smaller Java Image using Docker Multi-stage Build](http://blog.arungupta.me/smaller-java-image-docker-multi-stage-build/).

**NOTE:** 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.

1. Use Docker to build the sample code into a container, then push the container to the Docker registry:

   ```shell
   # Build the container on your local machine
   docker build -t {username}/helloworld-java-spring .

   # Push the container to docker registry
   docker push {username}/helloworld-java-spring
   ```
## Deploying the app

After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.

   {{< tabs name="helloworld_java_spring" default="kn" >}}
   {{% tab name="yaml" %}}

   1. 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.

      ```yaml
      apiVersion: serving.knative.dev/v1
      kind: Service
      metadata:
        name: helloworld-java-spring
        namespace: default
      spec:
        template:
          spec:
            containers:
              - image: docker.io/{username}/helloworld-java-spring
                env:
                  - name: TARGET
                    value: "Java Spring Sample v1"
      ```

   Ensure that the container image value
   in `service.yaml` matches the container you built in the previous step. Apply
   the configuration using `kubectl`:

   ```shell
   kubectl apply --filename service.yaml
   ```

   {{< /tab >}}
   {{% tab name="kn" %}}

   With `kn` you can deploy the service with

   ```shell
   kn service create helloworld-java-spring --image=docker.io/{username}/helloworld-java-spring --env TARGET="Java Spring Sample v1"
   ```

   This will wait until your service is deployed and ready, and ultimately it will print the URL through which you can access the service.

   {{< /tab >}}
   {{< /tabs >}}

   During the creation of your service, Knative performs the following steps:

   - Create a new immutable revision for this version of the app.
   - Network programming to create a route, ingress, service, and load balance
     for your app.
   - Automatically scale your pods up and down, including scaling down to zero active pods.

## Verification

1. Find the domain URL for your service:

   {{< tabs name="service_url" default="kn" >}}
   {{% tab name="kubectl" %}}
   ```shell
   kubectl get ksvc helloworld-java-spring  --output=custom-columns=NAME:.metadata.name,URL:.status.url
   ```

   Example:

   ```shell
   NAME                      URL
   helloworld-java-spring    http://helloworld-java-spring.default.1.2.3.4.xip.io
   ```

   {{< /tab >}}
   {{% tab name="kn" %}}

   ```shell
   kn service describe helloworld-java-spring -o url
   ```

   Example:

   ```shell
   http://helloworld-java-spring.default.1.2.3.4.xip.io
   ```
   {{< /tab >}}
   {{< /tabs >}}

1. Make a request to your app and observe the result. Replace
   the URL below with the URL returned in the previous command.

   Example:

   ```shell
   curl http://helloworld-java-spring.default.1.2.3.4.xip.io
   Hello Java Spring Sample v1!

   # Even easier with kn:
   curl $(kn service describe helloworld-java-spring -o url)
   ```

   > Note: Add `-v` option to get more detail if the `curl` command failed.

## Removing

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

{{< tabs name="service_url" default="kn" >}}
{{% tab name="kubectl" %}}
```shell
kubectl delete --filename service.yaml
```
{{< /tab >}}
{{% tab name="kn" %}}
```shell
kn service delete helloworld-java-spring
```
{{< /tab >}}
{{< /tabs >}}
