SparkJava on App Engine Flexible Environment

This app demonstrates how to use Datastore with the Google Cloud client library from within an App Engine flexible environment project using SparkJava. The app allows you to create and modify a database of "users", which contains their ID, name, and email information.

The Google Cloud client library is an idiomatic Java client for Google Cloud Platform services. Read more about the library here.

Setup

1. Create a Google Cloud project with the Datastore API enabled. Follow these instructions to get your project set up. If you wish to deploy this application, you will also need to enable billing.

2. Set up the local development environment by installing the Google Cloud SDK and running the following commands in command line: gcloud auth application-default login and gcloud config set project [YOUR PROJECT ID].

3. Ensure that you have Maven installed and configured to use Java 8. See installation instructions here.

Running locally

Run the application on your local machine by typing the following into your command line from the sparkjava directory: mvn clean package exec:java. Navigate to localhost:8080 to view and interact with the application.

Deploying

If you've enabled billing (step 1 in Setup), you can deploy the application to the web by running mvn appengine:deploy from your command line (from the sparkjava directory).

How does it work?

You'll notice that the source code is split into three folders: appengine, java/com/google/appengine/sparkdemo, and resource/public. The appengine folder contains a Dockerfile and an app.yaml, necessary files to configure the VM environment. The java/com/google/appengine/sparkdemo folder contains the controller code, which uses the Google Cloud client library to modify the records in the Google Cloud Datastore. Finally, the resource/public folder contains the home webpage, which uses jQuery to send HTTP requests to create, remove, and update records.

Spark runs the main method upon server startup. The main method creates the controller, UserController. The URIs used to send HTTP requests in the home page correspond to methods in the UserController class. For example, the index.html code for create makes a POST request to the path /api/users with a body containing the name and email of a user to add. UserController contains the following code to process that request:

post("/api/users", (req, res) -> userService.createUser(
    req.queryParams("name"),
    req.queryParams("email),
), json());

This code snippet gets the name and email of the user from the POST request and passes it to createUser (in UserService.java) to create a database record using the Google Cloud client library. If you want a more in-depth tutorial on using Google Cloud client library Datastore client, see the Getting Started section of the client library documentation.

Communication with the Google Cloud Datastore requires authentication and setting a project ID. When running locally, the Google Cloud client library automatically detects your credentials and project ID because you logged into the Google Cloud SDK and set your project ID. There are also many other options for authenticating and setting a project ID. To read more, see the Authentication and Specifying a Project ID sections of the client library documentation.

You built and ran this application using Maven. To read more about using Maven with App Engine flexible environment, see the Using Apache Maven documentation. While this particular project uses Maven, the Google Cloud client library packages can also be accessed using Gradle and SBT. See how to obtain the dependency in the Quickstart section of the client library documentation.

License

Apache 2.0 - See LICENSE for more information.