Quickstart for Java in the App Engine Flexible Environment

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

Before you begin

Before running this sample, take the following steps:

  1. Use the Cloud Platform Console to create a new Cloud Platform project, create an App Engine application, and enable billing:
    Go to App Engine

    When prompted, select the region where you want your App Engine application located and then enable billing.

  2. Install the following prerequisites :
    1. Download and install git.
    2. This quickstart uses Apache Maven to build, run, and deploy the sample app. For details about installing Maven, see Using Apache Maven and the App Engine Plugin.

This quickstart assumes that you have installed Java SE Runtime Environment 8

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 Google Cloud Platform. Follow these steps from a command line to download Hello World to your local machine.

Download the sample app and navigate into the app directory:

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

    git clone https://github.com/GoogleCloudPlatform/getting-started-java
    

    Alternatively, you can download the sample as a zip file and extract it.

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

    cd getting-started-java/helloworld-servlet
    

Run Hello World on your local machine

To run the Hello World app on your local computer:

  1. Start the local Jetty web server using the Jetty Maven plugin:

    mvn jetty:run-exploded
    
  2. In your web browser, enter the following address:

    http://localhost:8080
    

You can see the Hello World message from the sample app displayed in 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. Visit the following address to see your deployed app:
    https://[YOUR_PROJECT_ID].appspot.com

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!

Clean up

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

  1. In the Cloud Platform 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 project. After selecting the checkbox next to the project name, click
      Delete project
  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 stretch out and see the rest of Google Cloud Platform. You already have the Google Cloud SDK installed and that gives you the tools to interact with products like Google Cloud SQL, Google Cloud Storage, Google Cloud Datastore, and more. For a guided walkthrough that teaches you how to create an application 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 application's deployment configuration:

runtime: java
env: flex

handlers:
- url: /.*
  script: this field is required, but ignored
  secure: always  # Require HTTPS

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 like 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>1.0.0</appengine.maven.plugin>
    <jetty.maven.plugin>9.3.8.v20160314</jetty.maven.plugin>
  </properties>

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

  <prerequisites>                       <!-- Optional, but suggested -->
    <maven>3.3.9</maven>                <!-- Recommended minimum maven version -->
  </prerequisites>

  <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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