From 656d260a8386912a01e778a20370142d6c2fe002 Mon Sep 17 00:00:00 2001
From: Murugappan Chetty <itsmurugappan@gmail.com>
Date: Wed, 4 Nov 2020 10:24:06 -0800
Subject: [PATCH] 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
---
 .../helloworld-java-spring/index.md           | 242 +++++++++++++++++-
 1 file changed, 241 insertions(+), 1 deletion(-)

diff --git a/docs/serving/samples/hello-world/helloworld-java-spring/index.md b/docs/serving/samples/hello-world/helloworld-java-spring/index.md
index 718513d47..0dd0feef8 100644
--- a/docs/serving/samples/hello-world/helloworld-java-spring/index.md
+++ b/docs/serving/samples/hello-world/helloworld-java-spring/index.md
@@ -5,4 +5,244 @@ weight: 1
 type: "docs"
 ---
 
-{{% readfile file="README.md" %}}
+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 >}}