Using Gradle and the App Engine Plugin

Gradle is an open-source build automation tool focused on flexibility and performance. App Engine provides a Gradle plugin that you can use to build and deploy your app to App Engine. The code samples in this guide use Gradle version 8.

The code sample demonstrates how to configure the build.gradle file to add App Engine Gradle tasks, Maven repositories, App Engine Gradle plugin, and dependencies for Java 8. For Java version 11 and later, see Java runtime for more information about using newer versions.

Before you begin

  1. Install Java

  2. Install Gradle

  3. Install git

  4. If you haven't already done so, follow the steps in this guide to download the gcloud CLI, create your Google Cloud project, and initialize your App Engine app.

  5. Install the gcloud CLI app-engine-java component:

    gcloud components install app-engine-java

Create a new Gradle project

You can create a new Gradle project from scratch using the shell. Alternatively, to try out the plugin, you can download, run locally, and deploy the hello world project.

To create a new project:

  1. Create a new directory and navigate to it.

  2. To initialize a new project:

    1. Run gradle init:

      gradle init --type java-application

      You'll be asked to answer questions:

      • Enter target Java version (min: 7, default: 21): 21
      • Select application structure: 1 for Single application project
      • Select build script DSL: 2 (for Groovy)
      • Select test framework: 1 (for JUnit 4)
      • Generate build using new APIs and behavior: no

    2. Create the WEB-INF folder:

      mkdir -p app/src/main/webapp/WEB-INF

    3. Create the appengine folder:

      mkdir -p app/src/main/appengine

  3. Remove the stub files generated by gradle init:

    rm ./app/src/main/java/org/example/App.java ./app/src/test/java/org/example/AppTest.java

  4. Add the following to your app/build.gradle file to add App Engine Gradle tasks, Maven repositories, the App Engine Gradle plugin, dependencies, and task configuration: 

    buildscript {      // Configuration for building
  repositories {
    jcenter()      // Bintray's repository - a fast Maven Central mirror & more
    mavenCentral()
  }
  dependencies {
    classpath 'com.google.cloud.tools:appengine-gradle-plugin:2.5.0'
    classpath 'org.akhikhl.gretty:gretty:+'
  }
}

repositories {   // repositories for Jar's you access in your code
  jcenter()
  mavenCentral()
}

apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'org.akhikhl.gretty'
apply plugin: 'com.google.cloud.tools.appengine'

dependencies {
  providedCompile 'javax.servlet:javax.servlet-api:3.1.0'
  providedCompile 'com.google.appengine:appengine:+'
// Add your dependencies here.

}

gretty {
    servletContainer = 'jetty9'  // What App Engine Flexible uses
}

  appengine {
    deploy {   // deploy configuration
      stopPreviousVersion = true  // default - stop the current version
      promote = true              // default - & make this the current version
    }
  }

group = 'com.example.appengine'   // Generated output GroupId
version = '1.0-SNAPSHOT'          // Version in generated output

sourceCompatibility = 1.8
targetCompatibility = 1.8

  5. You also need to add the following files to your project, using a text editor or integrated development environment (IDE):

See Set up your development environment for an overview of a Java App Engine project.

Testing your application with the development server

  1. To access Google resources from your project when running locally, set the application default credentials by running:

    gcloud auth application-default login

  2. Change to the root of your application directory.

  3. During the development phase, you can run and test your application at any time in the development server by invoking Gradle:

    gradle jettyRun

    Alternatively, you can run Gradle without installing it by using the Gradle wrapper.

  4. Wait for the server to start. The server is started with your application running when you see a message similar to this:

    :prepareInplaceWebAppFolder
:createInplaceWebAppFolder
:compileJava
:processResources UP-TO-DATE
:classes
:prepareInplaceWebAppClasses
:prepareInplaceWebApp
:jettyRun
17:40:05 INFO  Jetty 9.2.15.v20160210 started and listening on port 8080
17:40:05 INFO   runs at:
17:40:05 INFO    http://localhost:8080/

  5. See your app running at http://localhost:8080.

To learn more about the Gretty plugin, see Gretty Configuration and Gretty tasks.

Deploy your application

To deploy your application:

gradle appengineDeploy

The appengineDeploy task and all other Gradle tasks have associated properties that you can use. For a complete list of tasks and properties, refer to App Engine Gradle Tasks and Properties.

Use the Gradle wrapper

Gradle provides a mechanism to download and run the required version of Gradle without installation:

Linux/macOS

  1. Change to the sample code directory.

  2. Run gradlew:

    ./gradlew jettyRun

Windows

  1. Change to the sample code directory.

  2. Run gradlew:

    ./gradlew.bat jettyRun

Additional information on Gradle can be found in App Engine Gradle Tasks and Properties.

What's next