# SparkJava on App Engine Flexible Environment Open in Cloud Shell This app demonstrates how to use [Datastore with the Google Cloud client library](https://github.com/GoogleCloudPlatform/google-cloud-java/tree/master/google-cloud-datastore) from within an [App Engine flexible environment](https://cloud.google.com/appengine/docs/flexible/java/hello-world) project using [SparkJava](http://sparkjava.com/). 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](https://cloud.google.com/) services. Read more about the library [here](https://github.com/GoogleCloudPlatform/google-cloud-java). Setup ----- 1. Create a Google Cloud project with the Datastore API enabled. [Follow these instructions](https://cloud.google.com/docs/authentication#preparation) to get your project set up. If you wish to deploy this application, you will also need to [enable billing](https://support.google.com/cloud/?rd=2#topic=6288636). 2. Set up the local development environment by [installing the Google Cloud SDK](https://cloud.google.com/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](https://maven.apache.org/install.html). 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](#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](https://cloud.google.com/appengine/docs/managed-vms/config). 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](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/managedvms/sparkjava-demo/src/main/java/com/google/appengine/sparkdemo/Main.java) upon server startup. The `main` method creates the controller, [`UserController`](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/managedvms/sparkjava-demo/src/main/java/com/google/appengine/sparkdemo/UserController.java). The URIs used to send HTTP requests in the [home page](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/managedvms/sparkjava-demo/src/main/resources/public/index.html) 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: ```java 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`](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/managedvms/sparkjava-demo/src/main/java/com/google/appengine/sparkdemo/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](https://github.com/GoogleCloudPlatform/google-cloud-java/tree/master/google-cloud-datastore#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](https://github.com/GoogleCloudPlatform/google-cloud-java#authentication) and [Specifying a Project ID](https://github.com/GoogleCloudPlatform/google-cloud-java#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](https://cloud.google.com/appengine/docs/flexible/java/using-maven). 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](https://github.com/GoogleCloudPlatform/google-cloud-java#quickstart) of the client library documentation. License ------- Apache 2.0 - See [LICENSE](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/master/LICENSE) for more information.