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hello world java with tabs (#2833)
* rewrite hello world java with tabs * rewrite hello world java with tabs * rewrite hello world java with tabs * review comments
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Murugappan Chetty
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@ -5,4 +5,244 @@ weight: 1
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type: "docs"
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---
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{{% readfile file="README.md" %}}
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This guide describes the steps required to create the `helloworld-java-spring` sample app and deploy it to your cluster.
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The sample app reads a `TARGET` environment variable, and prints `Hello ${TARGET}!`. If `TARGET` is not specified, `World` is used as the default value.
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You can also download a working copy of the sample, by running the following commands:
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```shell
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git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
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cd knative-docs/docs/serving/samples/hello-world/helloworld-java-spring
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```
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## Prerequisites
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- A Kubernetes cluster with Knative installed and DNS configured. Follow the
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[installation instructions](../../../../install/README.md).
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- [Docker](https://www.docker.com) installed and running on your local machine,
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and a Docker Hub account configured.
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- (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.
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## Building the sample app
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1. From the console, create a new, empty web project by using the curl and unzip
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commands:
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```shell
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curl https://start.spring.io/starter.zip \
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-d dependencies=web \
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-d name=helloworld \
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-d artifactId=helloworld \
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-o helloworld.zip
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unzip helloworld.zip
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```
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If you don't have `curl` installed, you can accomplish the same by visiting the
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[Spring Initializr](https://start.spring.io/) page. Specify Artifact as
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`helloworld` and add the `Web` dependency. Then click `Generate Project`,
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download and unzip the sample archive.
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1. Update the `SpringBootApplication` class in
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`src/main/java/com/example/helloworld/HelloworldApplication.java` by adding a
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`@RestController` to handle the "/" mapping and also add a `@Value` field to
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provide the `TARGET` environment variable:
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```java
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package com.example.helloworld;
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import org.springframework.beans.factory.annotation.Value;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.web.bind.annotation.GetMapping;
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import org.springframework.web.bind.annotation.RestController;
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@SpringBootApplication
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public class HelloworldApplication {
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@Value("${TARGET:World}")
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String target;
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@RestController
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class HelloworldController {
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@GetMapping("/")
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String hello() {
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return "Hello " + target + "!";
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}
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}
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public static void main(String[] args) {
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SpringApplication.run(HelloworldApplication.class, args);
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}
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}
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```
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1. Run the application locally:
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```shell
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./mvnw package && java -jar target/helloworld-0.0.1-SNAPSHOT.jar
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```
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Go to `http://localhost:8080/` to see your `Hello World!` message.
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1. In your project directory, create a file named `Dockerfile` and copy the code block below into it:
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```docker
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# Use the official maven/Java 8 image to create a build artifact.
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# https://hub.docker.com/_/maven
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FROM maven:3.5-jdk-8-alpine as builder
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# Copy local code to the container image.
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WORKDIR /app
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COPY pom.xml .
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COPY src ./src
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# Build a release artifact.
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RUN mvn package -DskipTests
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# Use AdoptOpenJDK for base image.
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# It's important to use OpenJDK 8u191 or above that has container support enabled.
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# https://hub.docker.com/r/adoptopenjdk/openjdk8
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# https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
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FROM adoptopenjdk/openjdk8:jdk8u202-b08-alpine-slim
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# Copy the jar to the production image from the builder stage.
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COPY --from=builder /app/target/helloworld-*.jar /helloworld.jar
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# Run the web service on container startup.
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CMD ["java", "-Djava.security.egd=file:/dev/./urandom", "-jar", "/helloworld.jar"]
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```
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For detailed instructions on dockerizing a Spring Boot app, see [Spring Boot with Docker](https://spring.io/guides/gs/spring-boot-docker/).
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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/).
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**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.
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1. Use Docker to build the sample code into a container, then push the container to the Docker registry:
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```shell
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# Build the container on your local machine
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docker build -t {username}/helloworld-java-spring .
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# Push the container to docker registry
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docker push {username}/helloworld-java-spring
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```
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## Deploying the app
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After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.
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{{< tabs name="helloworld_java_spring" default="kn" >}}
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{{% tab name="yaml" %}}
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1. Create a new file, `service.yaml` and copy the following service definition
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into the file. Make sure to replace `{username}` with your Docker Hub
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username.
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```yaml
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apiVersion: serving.knative.dev/v1
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kind: Service
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metadata:
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name: helloworld-java-spring
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namespace: default
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spec:
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template:
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spec:
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containers:
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- image: docker.io/{username}/helloworld-java-spring
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env:
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- name: TARGET
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value: "Java Spring Sample v1"
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```
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Ensure that the container image value
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in `service.yaml` matches the container you built in the previous step. Apply
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the configuration using `kubectl`:
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```shell
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kubectl apply --filename service.yaml
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```
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{{< /tab >}}
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{{% tab name="kn" %}}
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With `kn` you can deploy the service with
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```shell
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kn service create helloworld-java-spring --image=docker.io/{username}/helloworld-java-spring --env TARGET="Java Spring Sample v1"
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```
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This will wait until your service is deployed and ready, and ultimately it will print the URL through which you can access the service.
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{{< /tab >}}
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{{< /tabs >}}
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During the creation of your service, Knative performs the following steps:
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- Create a new immutable revision for this version of the app.
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- Network programming to create a route, ingress, service, and load balance
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for your app.
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- Automatically scale your pods up and down, including scaling down to zero active pods.
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## Verification
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1. Find the domain URL for your service:
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{{< tabs name="service_url" default="kn" >}}
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{{% tab name="kubectl" %}}
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```shell
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kubectl get ksvc helloworld-java-spring --output=custom-columns=NAME:.metadata.name,URL:.status.url
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```
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Example:
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```shell
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NAME URL
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helloworld-java-spring http://helloworld-java-spring.default.1.2.3.4.xip.io
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```
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{{< /tab >}}
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{{% tab name="kn" %}}
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```shell
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kn service describe helloworld-java-spring -o url
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```
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Example:
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```shell
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http://helloworld-java-spring.default.1.2.3.4.xip.io
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```
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{{< /tab >}}
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{{< /tabs >}}
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1. Make a request to your app and observe the result. Replace
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the URL below with the URL returned in the previous command.
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Example:
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```shell
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curl http://helloworld-java-spring.default.1.2.3.4.xip.io
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Hello Java Spring Sample v1!
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# Even easier with kn:
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curl $(kn service describe helloworld-java-spring -o url)
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```
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> Note: Add `-v` option to get more detail if the `curl` command failed.
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## Removing
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To remove the sample app from your cluster, delete the service record.
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{{< tabs name="service_url" default="kn" >}}
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{{% tab name="kubectl" %}}
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```shell
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kubectl delete --filename service.yaml
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```
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{{< /tab >}}
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{{% tab name="kn" %}}
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```shell
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kn service delete helloworld-java-spring
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```
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{{< /tab >}}
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{{< /tabs >}}
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