Using Gradle and the App Engine Plugin

You can use Gradle, a flexible build automation system that is declarative and is used to automate build, testing, publishing, and deployment. This page explains how to use Gradle with an App Engine project in the standard environment.

Before you begin

Install and configure the following prerequisites:

Setting up and validating your Cloud Platform project

You need to set up your Cloud Platform project and install the Cloud SDK:

  1. Use the Google Cloud Platform Console to create and set up your Cloud Platform project:

    Go to App Engine

    1. Select or create a new Cloud Platform project.
    2. Follow the prompts to ensure that an App Engine application exists and billing is enabled:
      1. If you need to create an App Engine application for your project, you are prompted to select the region where you want your App Engine application located.
      2. If you need to enable billing for your project, you are prompted to create a new billing account or select an existing account.
    3. The Dashboard opens after your App Engine application has been created and billing has been enabled in your project.
  2. Install and initialize the Google Cloud SDK.

    If you already have the gcloud tool installed and want to configure it to use a Cloud Platform project ID other than the one that you initialized it to, see Managing Cloud SDK Configurations.

  3. Install the App Engine SDK for Java:

    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.

  1. Create and enter a new directory.

  2. To initialize a new project:

    gradle init --type java-library;
    mkdir -p src/main/webapp/WEB-INF;
    rm src/main/java/Library.java src/test/java/LibraryTest.java
    
  3. 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:+'    // latest App Engine Gradle tasks
      }
    }
    
    repositories {   // repositories for Jar's you access in your code
      maven {
        url 'https://maven-central.storage.googleapis.com'             // Google's mirror of Maven Central
    //   url 'https://oss.sonatype.org/content/repositories/snapshots' // SNAPSHOT Repository (if needed)
      }
      jcenter()
      mavenCentral()
    }
    
    apply plugin: 'java'                              // standard Java tasks
    apply plugin: 'war'                               // standard Web Archive plugin
    apply plugin: 'com.google.cloud.tools.appengine'  // App Engine tasks
    
    dependencies {
      providedCompile group: 'javax.servlet', name: 'servlet-api', version:'2.5'
      compile 'com.google.appengine:appengine:+'
    // Add your dependencies here.
    
    }
    
    appengine {  // App Engine tasks configuration
      run {      // local (dev_appserver) configuration (standard environments only)
        port = 8080                 // default
      }
    
      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 = 1.7  // App Engine Standard uses Java 7
    targetCompatibility = 1.7  // App Engine Standard uses Java 7

  4. 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/appengine/helloworld-new-plugins
    

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 appengineRun
    

    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:

    :compileJava
    :processResources UP-TO-DATE
    :classes
    :war
    :explodeWar
    :assemble
    :appengineRun
    INFO     2016-08-16 19:44:52,131 devappserver2.py:769] Skipping SDK update check.
    INFO     2016-08-16 19:44:52,174 api_server.py:205] Starting API server at: http://localhost:62837
    INFO     2016-08-16 19:44:52,176 dispatcher.py:197] Starting module "default" running at: http://127.0.0.1:8080
    INFO     2016-08-16 19:44:52,178 admin_server.py:116] Starting admin server at: http://localhost:8000
    

  5. See your app running at http://127.0.0.1:8080.

Debugging on the development server

To debug a locally running application, set the jvmFlags property to enable debugging on the underlying JVM, for example:

    appengine {
      run {
        jvmFlags = ['-Xdebug', '-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005']
      }
    }

Enable hot reload of the application

Hot Reloading is the ability to update one or more classes in an application that is currently running without stopping the environment. To enable hot reload:

  • You must tell the local server to scan for changes:

    appengine {
      run {
        jvmFlags = ["-Dappengine.fullscan.seconds=5"]
      }
    }
    
  • You can either use explodeApp which clears and rebuilds the output directory or you can configure a new reloadApp task to rebuild into the exploded-<project> directory without deleting it.

    task reloadApp(type: Copy) {
      dependsOn war
    
      project.afterEvaluate {
        into project.tasks.explodeWar.explodedAppDirectory
         with war
      }
    }
    

While your application is running, run explodeApp or reloadApp to reflect your changes into the running application.

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:

Mac OS X and Linux

./gradlew appengineRun

Windows

gradlew.bat appengineRun

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

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App Engine standard environment for Java