Quickstart for Java in the App Engine Flexible Environment

This quickstart shows you how to create a small App Engine app that displays a short message.

Before you begin

This quickstart assumes that you have installed the Java SE 8 Development Kit (JDK).

Before running and deploying this quickstart, install the Cloud SDK and then set up a GCP project for App Engine:

  1. Download and install Cloud SDK:

    Download the SDK

    Note: If you already have the Cloud SDK installed, update it by running the following command:

    gcloud components update
    
  2. Create a new project:

    gcloud projects create [YOUR_PROJECT_ID] --set-as-default
    

    Verify the project was created:

    gcloud projects describe [YOUR_PROJECT_ID]
    

    You see project details that might look like the following:

    createTime: year-month-hour
    lifecycleState: ACTIVE
    name: project-name
    parent:
    id: '433637338589'
    type: organization
    projectId: project-name-id
    projectNumber: 499227785679
    
  3. Initialize your App Engine app with your project and choose its region:

    gcloud app create --project=[YOUR_PROJECT_ID]
    

    When prompted, select the region where you want your App Engine application located.

  4. Make sure billing is enabled for your project. A billing account needs to be linked to your project in order for the application to be deployed to App Engine.

    Enable billing

    Your flexible environment deployment will incur costs while it is active. Clean up your project when you are finished to avoid ongoing costs.

  5. Install the following prerequisites:

App Engine locations

App Engine is regional, which means the infrastructure that runs your apps is located in a specific region and is managed by Google to be redundantly available across all the zones within that region.

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 location of the other GCP products and services that are used by your app. Using services across multiple locations can affect your app's latency as well as pricing.

App Engine is available in the following regions:

  • northamerica-northeast1 (Montréal)
  • us-central (Iowa)
  • us-west2 (Los Angeles)
  • us-east1 (South Carolina)
  • us-east4 (Northern Virginia)
  • southamerica-east1 (São Paulo)
  • europe-west (Belgium)
  • europe-west2 (London)
  • europe-west3 (Frankfurt)
  • europe-west6 (Zürich)
  • asia-northeast1 (Tokyo)
  • asia-northeast2 (Osaka)
  • asia-east2 (Hong Kong)
  • asia-south1 (Mumbai)
  • australia-southeast1 (Sydney)

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

If you already created an App Engine application, you can view the region by running the gcloud app describe command or opening the App Engine Dashboard in the GCP Console. The region of your App Engine application is listed under http://[YOUR_PROJECT_ID].appspot.com.

Download the Hello World app

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

  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 as a zip file and extract it.

  2. Change to the directory that contains the sample code.

    cd java-docs-samples/flexible/helloworld
    

Run Hello World on your local machine

  1. Start the local Tomcat web server using the Spring Boot Maven plugin.

    mvn spring-boot:run
    
  2. In your web browser, enter the following address:

    http://localhost:8080

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:

  1. Deploy the Hello World app by running the following commands from the helloworld directory:

    gcloud config set project YOUR_PROJECT_ID
    mvn appengine:deploy
  2. Launch your browser to view the app at http://YOUR_PROJECT_ID.appspot.com

    gcloud app browse
    where YOUR_PROJECT_ID represents your GCP 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 Java app to App Engine flexible environment!

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 GCP project to stop billing for all the resources used within that project.

  1. In the GCP Console, go to the Projects page.

    Go to the Projects page

  2. In the project list, select the project you want to delete and click Delete .
  3. In the dialog, type the project ID, and then click Shut down to delete the project.

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 GCP. You already have the Cloud SDK installed which gives you the tools to interact with products like Cloud SQL, Cloud Storage, Cloud Firestore, and more.

For a guided walkthrough that teaches you how to create an app that uses the entire platform, not just App Engine, check out our quickstart on creating the Bookshelf app.

Learn about the App Engine flexible environment

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

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.

HelloServlet.java

The HelloServlet.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.

@SuppressWarnings("serial")
@WebServlet(name = "helloworld", value = "/")
public class HelloServlet extends HttpServlet {

  @Override
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    PrintWriter out = resp.getWriter();
    out.println("Hello, world - Flex Servlet");
  }
}

app.yaml

The app.yaml file describes an app's deployment configuration:

runtime: java
env: flex

handlers:
- url: /.*
  script: this field is required, but ignored

runtime_config:  # Optional
  jdk: openjdk8
  server: jetty9

manual_scaling:
  instances: 1

Here, app.yaml specifies the runtime used by the app, and sets env: flex, specifying that the app uses the flexible environment.

pom.xml

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

<project>                               <!-- REQUIRED -->

  <modelVersion>4.0.0</modelVersion>    <!-- REQUIRED -->
  <packaging>war</packaging>            <!-- REQUIRED -->

  <groupId>com.example.flex.helloworld</groupId>
  <artifactId>helloworld-servlet</artifactId> <!-- Name of your project -->
  <version>1.0-SNAPSHOT</version>       <!-- xx.xx.xx -SNAPSHOT means development -->

  <properties>
    <maven.compiler.source>1.8</maven.compiler.source> <!-- REQUIRED -->
    <maven.compiler.target>1.8</maven.compiler.target> <!-- REQUIRED -->
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

    <failOnMissingWebXml>false</failOnMissingWebXml> <!-- REQUIRED -->
    <appengine.maven.plugin>1.3.2</appengine.maven.plugin>
    <jetty.maven.plugin>9.4.3.v20170317</jetty.maven.plugin>
  </properties>

  <parent>                              <!-- Get parameters and allow bulk testing -->
    <artifactId>getting-started-java</artifactId>
    <groupId>com.example</groupId>
    <version>1.0.0</version>
    <relativePath>..</relativePath>
  </parent>

  <dependencies>
    <dependency>                        <!-- REQUIRED -->
      <groupId>javax.servlet</groupId>  <!-- Java Servlet API -->
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>           <!-- Provided by the Jetty Servlet Container -->
    </dependency>
  </dependencies>

  <build>
    <!-- For hot reload of the web application when using an IDE Eclipse / IDEA -->
    <outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>

    <plugins>

      <plugin>                          <!-- Used for local debugging -->
        <groupId>org.eclipse.jetty</groupId>
        <artifactId>jetty-maven-plugin</artifactId>
        <version>${jetty.maven.plugin}</version>
      </plugin>

      <plugin>
        <groupId>com.google.cloud.tools</groupId>
        <artifactId>appengine-maven-plugin</artifactId>
        <version>${appengine.maven.plugin}</version>
        <configuration>
          <!-- deploy configuration -->
<!--
          <deploy.promote>true</deploy.promote>                           <!~~ DEFAULT value ~~>
          <deploy.stopPreviousVersion>true</deploy.stopPreviousVersion>   <!~~ DEFAULT value ~~>
 -->
        </configuration>
      </plugin>

    </plugins>
  </build>
</project>
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