# Create a Java app in the App Engine flexible environment


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### Region ID

The `REGION_ID` is an abbreviated code that Google assigns
based on the region you select when you create your app. The code does not
correspond to a country or province, even though some region IDs may appear
similar to commonly used country and province codes. For apps created after
February 2020, `REGION_ID.r` is included in
App Engine URLs. For existing apps created before this date, the
region ID is optional in the URL.

Learn more
[about region IDs](https://docs.cloud.google.com/appengine/docs/flexible/java/how-requests-are-routed#region-id).
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> [!NOTE]
> **Note:** If you are deploying a new Java web service to Google Cloud, we recommend getting started with [Cloud Run](https://docs.cloud.google.com/run/docs/quickstarts/build-and-deploy/deploy-java-service).

This quickstart demonstrates how to create and deploy an app that displays a
short message. The sample application uses Java version 17.

## Before you begin

This quickstart assumes that you have installed the [Java SE 17 Development Kit (JDK) on your local machine](https://www.azul.com/downloads/zulu/).

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### Required roles


To get the permissions that
you need to complete this quickstart,

ask your administrator to grant you the
following IAM roles:

- [App Engine Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/appengine#appengine.appAdmin) (`roles/appengine.appAdmin`) on the project
- [Cloud Build Editor](https://docs.cloud.google.com/iam/docs/roles-permissions/cloudbuild#cloudbuild.builds.editor) (`roles/cloudbuild.builds.editor`) on the project
- [Storage Object Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/storage#storage.objectAdmin) (`roles/storage.objectAdmin`) on the project
- [Logs Viewer](https://docs.cloud.google.com/iam/docs/roles-permissions/logging#logging.viewer) (`roles/logging.viewer`) on the project
- [Service Account User](https://docs.cloud.google.com/iam/docs/roles-permissions/iam#iam.serviceAccountUser) (`roles/iam.serviceAccountUser`) on the service account
- Ask your administrator to grant the following roles for the App Engine default service account:
  - [Artifact Registry Reader](https://docs.cloud.google.com/iam/docs/roles-permissions/artifactregistry#artifactregistry.reader) (`roles/artifactregistry.reader`) on the project
  - [Cloud Build Service Account](https://docs.cloud.google.com/iam/docs/roles-permissions/cloudbuild#cloudbuild.builds.builder) (`roles/cloudbuild.builds.builder`) on the project
  - [Storage Object Viewer](https://docs.cloud.google.com/iam/docs/roles-permissions/storage#storage.objectViewer) (`roles/storage.objectViewer`) on the project


For more information about granting roles, see [Manage access to projects, folders, and organizations](https://docs.cloud.google.com/iam/docs/granting-changing-revoking-access).


You might also be able to get
the required permissions through [custom
roles](https://docs.cloud.google.com/iam/docs/creating-custom-roles) or other [predefined
roles](https://docs.cloud.google.com/iam/docs/roles-overview#predefined).

## Additional prerequisites

1. Initialize your App Engine app with your project and choose its region:

       gcloud app create --project=[YOUR_PROJECT_ID]

   When prompted, select the [region](https://docs.cloud.google.com/appengine/docs/flexible/locations)
   where you want to locate your App Engine application.

   > [!CAUTION]
   > **Caution**: You cannot change an app's region once it has been set.

2. Install the following on your local machine:

   - [Download
     and install Git](https://git-scm.com/).
   - [Download and install Maven 3.5 or greater](https://maven.apache.org/install.html). This quickstart uses Apache Maven version 3.5 or greater to build and run the sample app on your computer.

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### App Engine locations

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App Engine is *regional* , which means the infrastructure that runs your apps is
located in a specific region, and Google manages it so that it is available
redundantly across
[all of the zones within that region](https://docs.cloud.google.com/docs/geography-and-regions).

Meeting your latency, availability, or durability requirements are primary
factors for selecting the region where your apps are run. You can generally
select the region nearest to your app's users, but you should consider [the
locations where App Engine is available](https://cloud.google.com/about/locations/#region)
as well as the [locations](https://cloud.google.com/about/locations/#region) of the other
Google Cloud products and services that your app uses. Using services
across multiple locations can affect your app's latency as well as its
[pricing](https://cloud.google.com/appengine/pricing).

You cannot change an app's region after you set it.

> [!NOTE]
> **Note:** Two locations, which are called `europe-west` and `us-central` in App Engine commands and in the Google Cloud console, are called `europe-west1` and `us-central1`, respectively, elsewhere in Google documentation.

If you already created an App Engine application, you can view its
region by doing one of the following:

- Run the `gcloud app describe` command.

- Open the
  [App Engine Dashboard in the Google Cloud console](https://console.cloud.google.com/appengine).
  The region appears near the top of the page.

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## Download the Hello World app

We've created a Hello World app for App Engine so you can quickly
get a feel for deploying an app to the Google Cloud.

1. Clone the Hello World sample app repository to your local machine.

       git clone https://github.com/GoogleCloudPlatform/java-docs-samples


   Alternatively, you can [download the sample](https://github.com/GoogleCloudPlatform/java-docs-samples/archive/master.zip) as a zip file and extract it.
2. Change to the directory that contains the sample code.

          cd java-docs-samples/flexible/java-17/micronaut-helloworld

## Run Hello World on your local machine

To run the Hello World app on your local computer:

1. Run the following command:

   ```
   java -jar target/micronaut-helloworld-0.1.jar
   ```
2. In your web browser, enter the following address:

   <http://localhost:8080>

   If you are using Cloud Shell, in the toolbar, click
   **Web Preview** ![](https://docs.cloud.google.com/static/shell/docs/images/web-preview-button.png)
   and select **Preview on port 8080** instead.

The **Hello World** message from the sample app displays on the page. In your
terminal window, press **Ctrl+C** to exit the web server.

## Deploy and run Hello World on App Engine

To deploy your app to the App Engine flexible environment:

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1.
   Deploy the Hello World app by running the following
   command from the `java-17/micronaut-helloworld` directory:

   ```bash
   mvn clean package appengine:deploy
   ```
2.
   Launch your browser to view the app at

   `https://PROJECT_ID.https://docs.cloud.google.com/appengine/docs/flexible/java/create-app#appengine-urls.r.appspot.com`

   ```bash
   gcloud app browse
   ```
   where `PROJECT_ID` represents your Google Cloud project ID.


This time, the page that displays the Hello World message is delivered by a
web server running on an App Engine instance.

**Congratulations!** You've deployed your first App Engine app to the
App Engine flexible environment!
If you encountered any errors deploying your application, check the [troubleshooting tips](https://docs.cloud.google.com/appengine/docs/flexible/testing-and-deploying-your-app#troubleshooting).

See the following sections for information about cleaning up as well as links to
possible next steps that you can take.

## Clean up

To avoid incurring charges, you can delete your Google Cloud project to stop
billing for all the resources used within that project.

> [!CAUTION]
> **Caution** : Deleting a project has the following effects:
>
> - **Everything in the project is deleted.** If you used an existing project for the tasks in this document, when you delete it, you also delete any other work you've done in the project.
> - **Custom project IDs are lost.** When you created this project, you might have created a custom project ID that you want to use in the future. To preserve the URLs that use the project ID, such as an `appspot.com` URL, delete selected resources inside the project instead of deleting the whole project.

1. In the Google Cloud console, go to the **Manage resources** page.

   [Go to Manage resources](https://console.cloud.google.com/iam-admin/projects)
2. In the project list, select the project that you want to delete, and then click **Delete**.
3. In the dialog, type the project ID, and then click **Shut down** to delete the project.

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## What's next

#### Learn the whole platform

Now that you know what it's like to develop and deploy App Engine apps,
you can explore the rest of Google Cloud. You already have the
Google Cloud CLI installed which gives you the tools to interact with
products like Cloud SQL, Cloud Storage, Firestore,
and more.

#### Learn about the App Engine flexible environment

Here are some topics to help continue your learning about App Engine:

- [An overview of App Engine](https://docs.cloud.google.com/appengine/docs/flexible/an-overview-of-app-engine)
- [Request routing](https://docs.cloud.google.com/appengine/docs/flexible/how-requests-are-routed)
- [Request handling](https://docs.cloud.google.com/appengine/docs/flexible/how-requests-are-handled)
- [Managing instances](https://docs.cloud.google.com/appengine/docs/flexible/how-instances-are-managed)

## Hello World code review

Hello World is the simplest possible App Engine app, as it contains only
one service, has only one version, and all of the code is located within the
app's root directory. This section describes each of the app files in detail.

#### `HelloControllerTest.java`

The `HelloControllerTest.java` file specifies a URL pattern that describes where the
app will listen for requests, and responds to any requests with the 'Hello
World' message.

    /*
     * Copyright 2023 Google LLC
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     * http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    package com.example.appengine;

    import static org.junit.Assert.assertEquals;

    import io.micronaut.context.ApplicationContext;
    import io.micronaut.http.HttpRequest;
    import io.micronaut.http.client.HttpClient;
    import io.micronaut.runtime.server.EmbeddedServer;
    import org.junit.AfterClass;
    import org.junit.BeforeClass;
    import org.junit.Test;

    public class HelloControllerTest {
      private static EmbeddedServer server;
      private static HttpClient client;

      @BeforeClass
      public static void setupServer() {

        server = ApplicationContext.run(EmbeddedServer.class);

        client = server.getApplicationContext().createBean(HttpClient.class, server.getURL());
      }

      @AfterClass
      public static void stopServer() {
        if (client != null) {
          client.stop();
        }
        if (server != null) {
          server.stop();
        }
      }

      @Test
      public void testHelloWorldResponse() {
        String response = client.toBlocking().retrieve(HttpRequest.GET("/"));
        assertEquals("Hello World!", response);
      }
    }

#### `app.yaml`

The [`app.yaml`](https://docs.cloud.google.com/appengine/docs/flexible/java/configuring-your-app-with-app-yaml)
file describes the following configuration for your app:

- Sets `env: flex`, indicating your app uses the [App Engine flexible environment](https://docs.cloud.google.com/appengine/docs/flexible).
- Specifies the runtime used by the app.


      runtime: java
      env: flex
      runtime_config:
        operating_system: ubuntu22
        runtime_version: 17
      handlers:
      - url: /.*
        script: this field is required, but ignored

      manual_scaling:
        instances: 1

  - For more information on how the Java runtime works, see [The Java runtime](https://docs.cloud.google.com/appengine/docs/flexible/java/runtime).

  #### `pom.xml`

  Hello World also includes a `pom.xml` file, which contains information about
  the project, such as its dependencies and the build target.

      <?xml version="1.0" encoding="UTF-8"?>
      <!--
        Copyright 2023 Google LLC
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.
        You may obtain a copy of the License at
             http://www.apache.org/licenses/LICENSE-2.0
        Unless required by applicable law or agreed to in writing, software
        distributed under the License is distributed on an "AS IS" BASIS,
        WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
        See the License for the specific language governing permissions and
        limitations under the License.
      -->
      <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>com.example.appengine.flexible</groupId>
        <artifactId>micronaut-helloworld</artifactId>
        <version>0.1</version>

        <!--
        The parent pom defines common style checks and testing strategies for our samples.
        Removing or replacing it should not affect the execution of the samples in anyway.
        -->
        <parent>
            <groupId>com.google.cloud.samples</groupId>
            <artifactId>shared-configuration</artifactId>
            <version>1.2.0</version>
        </parent>

        <properties>
          <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
          <exec.mainClass>com.example.appengine.Application</exec.mainClass>
          <maven.compiler.target>11</maven.compiler.target>
          <maven.compiler.source>11</maven.compiler.source>
          <micronaut.version>3.10.10</micronaut.version>
        </properties>

        <dependencies>
          <dependency>
            <groupId>io.micronaut</groupId>
            <artifactId>micronaut-inject</artifactId>
            <version>${micronaut.version}</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>io.micronaut</groupId>
            <artifactId>micronaut-validation</artifactId>
            <version>${micronaut.version}</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>io.micronaut</groupId>
            <artifactId>micronaut-runtime</artifactId>
            <version>${micronaut.version}</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>io.micronaut</groupId>
            <artifactId>micronaut-http-client</artifactId>
            <version>${micronaut.version}</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>javax.annotation</groupId>
            <artifactId>javax.annotation-api</artifactId>
            <version>1.3.2</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>io.micronaut</groupId>
            <artifactId>micronaut-http-server-netty</artifactId>
            <version>${micronaut.version}</version>
            <scope>compile</scope>
          </dependency>
          <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
          </dependency>
        </dependencies>

        <build>
          <plugins>
            <plugin>
              <groupId>com.google.cloud.tools</groupId>
              <artifactId>appengine-maven-plugin</artifactId>
              <version>2.8.0</version>
              <configuration>
                <projectId>GCLOUD_CONFIG</projectId>
                <version>micronaut-helloworld</version>
              </configuration>
            </plugin>
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-shade-plugin</artifactId>
              <version>3.5.1</version>
              <executions>
                <execution>
                  <phase>package</phase>
                  <goals>
                    <goal>shade</goal>
                  </goals>
                  <configuration>
                    <transformers>
                      <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                        <mainClass>${exec.mainClass}</mainClass>
                      </transformer>
                      <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                    </transformers>
                  </configuration>
                </execution>
              </executions>
            </plugin>
            <plugin>
              <groupId>org.codehaus.mojo</groupId>
              <artifactId>exec-maven-plugin</artifactId>
              <version>3.1.1</version>
              <configuration>
                <executable>java</executable>
                <arguments>
                  <argument>-noverify</argument>
                  <argument>-XX:TieredStopAtLevel=1</argument>
                  <argument>-Dcom.sun.management.jmxremote</argument>
                  <argument>-classpath</argument>
                  <classpath/>
                  <argument>${exec.mainClass}</argument>
                </arguments>
              </configuration>
            </plugin>
            <plugin>
              <artifactId>maven-surefire-plugin</artifactId>
              <version>3.2.5</version>
            </plugin>

              <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.12.1</version>
                <configuration>
                  <encoding>UTF-8</encoding>
                  <compilerArgs>
                    <arg>-parameters</arg>
                  </compilerArgs>
                  <annotationProcessorPaths>
                    <path>
                      <groupId>io.micronaut</groupId>
                      <artifactId>micronaut-inject-java</artifactId>
                      <version>${micronaut.version}</version>
                    </path>
                    <path>
                      <groupId>io.micronaut</groupId>
                      <artifactId>micronaut-validation</artifactId>
                      <version>${micronaut.version}</version>
                    </path>
                  </annotationProcessorPaths>
                </configuration>
                <executions>
                  <execution>
                    <id>test-compile</id>
                    <goals>
                      <goal>testCompile</goal>
                    </goals>
                    <configuration>
                      <compilerArgs>
                        <arg>-parameters</arg>
                      </compilerArgs>
                      <annotationProcessorPaths>
                        <path>
                          <groupId>io.micronaut</groupId>
                          <artifactId>micronaut-inject-java</artifactId>
                          <version>${micronaut.version}</version>
                        </path>
                        <path>
                          <groupId>io.micronaut</groupId>
                          <artifactId>micronaut-validation</artifactId>
                          <version>${micronaut.version}</version>
                        </path>
                      </annotationProcessorPaths>
                    </configuration>
                  </execution>
                </executions>
              </plugin>
            </plugins>

        </build>
      </project>

  - For more information about `pom.xml` files, see the [Maven documentation](https://maven.apache.org/guides/introduction/introduction-to-the-pom.html).