This sample demonstrates how to use Websockets on Google App Engine Flexible Environment using Java. The sample uses the native Jetty WebSocket Server API to create a server-side socket and the native Jetty WebSocket Client API.

1. The sample application creates a server socket using the endpoint /echo.
2. The homepage (/) provides a form to submit a text message to the server socket. This creates a client-side socket and sends the message to the server.
3. The server on receiving the message, echoes the message back to the client.
4. The message received by the client is stored in an in-memory cache and is viewable on the homepage.

The sample also provides a Javascript client(/js_client.jsp) that you can use to test against the Websocket server.

• Install and initialize GCloud SDK. This will

   gcloud init

• If this is your first time creating an app engine application

  gcloud appengine create

Run using the Jetty Maven plugin.

mvn jetty:run

You can then direct your browser to http://localhost:8080/

To test the Javascript client, access http://localhost:8080/js_client.jsp

App Engine Flex deployment configuration is provided in app.yaml.

Set the environment variable JETTY_MODULES_ENABLE:websocket to enable the Jetty websocket module on the Jetty server.

Manual scaling is set to a single instance as we are using an in-memory cache of messages for this sample application.

For more details on configuring your app.yaml, please refer to this resource.

The sample application is packaged as a war, and hence will be automatically run using the Java 8/Jetty 9 with Servlet 3.1 Runtime.

mvn appengine:deploy

You can then direct your browser to https://YOUR_PROJECT_ID.appspot.com/

To test the Javascript client, access https://YOUR_PROJECT_ID.appspot.com/js_client.jsp

Note: This application constructs a Web Socket URL using getWebSocketAddress in the SendServlet Class . The application assumes the latest version of the service.