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.

Before you begin

  1. Install Java

  2. Install Gradle (v3.4.1 or newer)

  3. Install git

  4. If you haven't already done so, follow the steps in the Quickstart to download the Cloud SDK, create your Cloud project, and initialize your App Engine app.

  5. Install the Cloud SDK app-engine-java component:

    gcloud components install app-engine-java
    

Creating 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-library
      
    2. Create the WEB-INF folder:

      mkdir -p src/main/webapp/WEB-INF
      
    3. Create the appengine folder:

      mkdir -p src/main/appengine
      
  3. Remove the stub files generated by gradle init:

    rm src/main/java/Library.java src/test/java/LibraryTest.java
    
  4. Add the following to your 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:2.2.0'
        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 the quickstart for an overview of a Java App Engine project.

Downloading the Hello World app

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

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

    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
    

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.

Deploying 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.

Using 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