Using Apache Maven and the App Engine plugin (Google Cloud CLI-based)

This page explains how to manage an App Engine project for your Cloud Endpoints Frameworks API by using Apache Maven. Apache Maven is a software project management and comprehension tool capable of building Web Application Archive (WAR) files for deployment into App Engine. Google provides a plugin and Maven Archetypes that are supported by Maven 3.3.9 or greater.

Maven downloads the Java libraries from the App Engine SDK. You can use Maven to test your app locally and deploy it to App Engine.

Before you start

Use the Google Cloud console to create and set up your Google Cloud project:

Go to App Engine
1. Select or create a new Google Cloud project.
2. If you need to create an App Engine application for your project, follow the prompts to select the region where you want your App Engine application located.
Download and install the gcloud CLI, and then initialize the Google Cloud CLI.
If you already have the Google Cloud CLI installed and want to set it to use a different Google Cloud project ID than the one that you initialized it to, see Managing gcloud CLI configurations.
Install the gcloud CLI app-engine-java component:
```
gcloud components install app-engine-java
```
Note: To make sure you have the latest version of the gcloud CLI for Java, run gcloud components update.
If you don't have Java, download, install, and configure it.

Set the Java compiler flags in your project's pom.xml to specify Java 8 byte code:

<properties>
  <maven.compiler.source>1.8</maven.compiler.source>
  <maven.compiler.target>1.8</maven.compiler.target>
</properties>

You must have Apache Maven version 3.3.9 or greater installed. To determine your Maven version, run the following command:
```
 mvn -v
```
If you don't have the proper version of Maven installed:
1. Download Maven version 3.3.9 or greater from the Maven website.
2. Install Maven on your local machine.
  Note: Linux users may need to download Maven instead of using apt-get install.

Adding the App Engine Maven plugin to an existing project (optional)

To use the App Engine Maven plugin in an existing Maven project, add the following to the plugins section in the project's pom.xml file:

<plugin>
   <groupId>com.google.cloud.tools</groupId>
   <artifactId>appengine-maven-plugin</artifactId>
   <version>2.8.1</version>
</plugin>

Choosing an App Engine archetype

Maven archetypes let users create Maven projects by using templates that cover common scenarios. App Engine takes advantage of this Maven feature to provide some useful App Engine archetypes at Maven Central. Select an App Engine archetype appropriate for your app:

Application type	Artifact	Description
Endpoints Frameworks for App Engine	`endpoints-skeleton-archetype`	Generates a new, empty Endpoints Frameworks for App Engine backend API project ready for your own classes and resources, with required files and directories.
Endpoints Frameworks for App Engine	`hello-endpoints-archetype`	Generates a starter Endpoints Frameworks for App Engine backend API project, ready to build and run.

Creating a new project by using Maven

During project creation, Maven prompts you to supply groupId, artifactId, version, and the package for the project.

Term	Meaning
`groupId`	A namespace within Maven to keep track of your artifacts. When people consume your project in their own Maven Project, it serves as an attribute of the dependency they end up specifying.
`artifactId`	The name of your project within Maven. It is also specified by consumers of your project when they depend on you in their own Maven projects.
`version`	The initial Maven version you want to have your project generated with. It's a good idea to have `version` suffixed by `-SNAPSHOT` because this provides support in the Maven release plugin for versions that are under development. For more information, see the Maven guide to using the release plugin.
`package`	The Java package created during the generation.

Creating a new Endpoints Frameworks app

This section describes creating a new Endpoints Frameworks version 2.0 project.

The hello-endpoints-archetype provides an example of using plugins, including the App Engine Maven plugin and Endpoints Frameworks Maven plugin.

The hello-endpoints-archetype generates an example Greetings API by using Endpoints Frameworks version 2.0. It also acts as an example for migrating your Endpoints Frameworks version 1.0 applications to Endpoints Frameworks version 2.0.

The README.md that's generated with the archetype provides information of where the migration occurred.

To create an Endpoints Frameworks for App Engine backend API archetype project:

Change directory to a directory where you want to build the project.
Run the following Maven command:
```
mvn archetype:generate -Dgoogle-cloud-project=[YOUR-PROJECT-ID] -Dappengine-plugin=2.8.1 -Dendpoints-frameworks=2.1.0 -Dendpoints-plugin=1.0.2 -Dappengine-sdk=1.9.98 -Dfilter=com.google.appengine.archetypes:
```
Where:
- -Dgoogle-cloud-project is set to your project ID.
- -Dappengine-plugin is set to the most recent version of the App Engine Maven plugin.
- -Dendpoints-frameworks is set to the most recent version of the Endpoints Frameworks for App Engine for Maven dependencies.
- -Dendpoints-plugin is set to the most recent version of the Endpoints Frameworks for App Engine Maven plugin.
Note: Endpoints Frameworks for App Engine archetypes have Gradle support and uses the latest version of each dependency.
Supply the number corresponding to hello-endpoints-archetype.

Note: To create an empty project containing the required directory structure and files ready for your own classes, supply the number corresponding to endpoints-skeleton-archetype.
Select the most recent version from the displayed list of available archetype versions.
When prompted to Define value for property 'groupId', supply the namespace for your app; for example, supply the value com.example.helloendpoints.
When prompted to Define value for property 'artifactId', supply the project name; for example, supply the value helloendpoints.
When prompted to Define value for property 'version', accept the default value.
When prompted to Define value for property 'package', accept the default value.
When prompted to confirm your choices, accept the default value by entering Y.
Wait for the project to finish generating. then change directories to the new project directory, for example helloendpoints/.
Build the project.
```
mvn clean package
```

Wait for the project to build. When the project successfully finishes, a message similar to the following is displayed:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.062 s
[INFO] Finished at: 2017-02-28T00:28:03-08:00
[INFO] Final Memory: 27M/485M
[INFO] ------------------------------------------------------------------------

To test locally and deploy the project to the App Engine standard environment, review Managing, testing, and deploying a Maven project.
Additionally, you can generate Java client libraries for the Greeting API by using the Endpoints Frameworks Maven Plugin:
```
mvn endpoints-framework:clientLibs
```

The following diagram shows the basic project layout of the Greetings API:

Maven Project Layout

README.md contains information about the generated example.
Greetings.java contains an API definition for an example Greetings API.
Constants.java contains constants used in by the example Greetings API.
HelloGreeting.java contains a container for messages received and sent from the example Greetings API.
index.html contains simple UI to call the backend Greetings API.
base.js contains necessary JavaScript for the UI to make backend requests.
build.gradle once generated, the example also supports Gradle and more information about this functionality in the README.md.

Compiling and building your application

To build an application created with the Maven App Engine archetypes:

Change to the main directory for your project, for example, guestbook/.
Run Maven:
```
mvn clean package
```
Wait for the project to build. When the project successfully finishes, a message similar to the following is displayed:
```
BUILD SUCCESS
 Total time: 10.724s
 Finished at: 2016-08-04T16:18:24-07:00
 Final Memory: 24M/213M
```

Testing your application with the development server

During the development phase, you can run and test your application at any time in the development server by running the App Engine Maven plugin.

To test your Endpoints Frameworks for App Engine app:

If you haven't already done so, build your app:
```
mvn clean package
```

Run the example locally:

mvn appengine:run

Wait for the server to start. When the server is completely started with your application running, a message similar to the following is displayed:

[INFO] GCLOUD: INFO ### devappserver2.py:764] Skipping SDK update check.
[INFO] GCLOUD: INFO ### api_server.py:268] Starting API server at: http://localhost:34199
[INFO] GCLOUD: INFO ### dispatcher.py:199] Starting module "default" running at: http://localhost:8080
[INFO] GCLOUD: INFO ### admin_server.py:116] Starting admin server at: http://localhost:8000
[INFO] GCLOUD: ### com.google.appengine.tools.development.SystemPropertiesManager setSystemProperties

Use your browser to go to http://localhost:8080/ to access your app.
Shut down the application and the development server by pressing Control+C.

Specifying a port for local testing

When you run your application in the local development server, the default port is 8080. You can change this default by modifying the plugin entry for appengine-maven-plugin. For example, you can specify port and address in the pom.xml file of your application directory:

<plugins>
   <plugin>
     <groupId>com.google.cloud.tools</groupId>
     <artifactId>appengine-maven-plugin</artifactId>
     <version>2.8.1</version>
     <configuration>
       <devserver.host>0.0.0.0</devserver.host>
       <devserver.port>8181</devserver.port>
     </configuration>
  </plugin>
</plugins>

In this example, the <devserver.port> sets the port to 8181 instead of the default, and the address 0.0.0.0 is specified, which means the development server listens for requests coming in from the local network.

The prefix devserver is optional; you can use <port>8181</port> instead.

Debugging on the development server

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

<configuration>
  <jvmFlags>
    <jvmFlag>-Xdebug</jvmFlag>
    <jvmFlag>-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005</jvmFlag>
  </jvmFlags>
</configuration>

Deploying your application

To deploy your application:

mvn appengine:deploy

The appengine:deploy goal and all other goals in the App Engine Maven plugin have associated parameters that you can use. For a complete list of goals and parameters, refer to App Engine Maven plugin goals and parameters.

What's next

Explore the App Engine Maven plugin code and report issues on GitHub.
Learn how to specify parameters for goals by referring to App Engine Maven Goals and Parameters.
Explore the Endpoints Frameworks Maven plugin code and report issues on GitHub.
Learn how to specify parameters for goals by referring to Cloud Endpoints Frameworks Maven plugin.