Walkthrough for creating a room in java for Game On!
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README.md

Game On! Microservices and Java

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Game On! is both a sample microservices application, and a throwback text adventure brought to you by the WASdev team at IBM. This application demonstrates how microservice architectures work from two points of view:

  1. As a Player: navigate through a network/maze of rooms, and interact with other players and the items or actions available in each room.
  2. As a Developer: extend the game by creating simple services that define rooms. Learn about microservice architectures and their supporting infrastructure as you build and scale your service.

You can learn more about Game On! at http://gameontext.org/.

Introduction

This walkthrough will guide you through creating and deploying a simple room (a microservice) to the running Game On! application. This microservice is written in Java as a web application deployed on Websphere Liberty.

The microservice can be (a) deployed as a Cloud Foundry application or (b) built into a docker container.

Game On! communicates with this service (a room) over WebSockets using the Game On! WebSocket protocol. Consider this a stand-in for asynchronous messaging like MQTT, which requires a lot more setup than a simple WebSocket does.

Requirements

Let's get started!

  1. Create your own fork of this repository (what's a fork?)
  2. Create a local clone of your fork (Cloning a repository)

Build the service locally

  1. cd sample-room-java
  2. mvn install
  3. mvn liberty:run-server

After running this, the server will be running locally at http://localhost:9080/.

  • Visiting this page provides a small form you can use to test the WebSocket endpoint in your service directly.
  • A health URL is also defined by the service, at http://localhost:9080/rest/health

Make your room public!

For Game On! to include your room, you need to tell it where the publicly reachable WebSocket endpoint is. This usually requires two steps:

Build a docker container

Creating a Docker image is straight-up: docker build . right from the root menu.

A docker-compose.yml file is also there, which can be used to specify overlay volumes to allow local development without restarting the container. See running with hot-reload for more details.

Ok. So this thing is running... Now what?

We know, this walkthrough was simple. You have a nice shiny service that has a REST API (/rest/health), and emulates async messaging behavior via a WebSocket. So?

The purpose of this text-based adventure is to help you grapple with microservices concepts and technologies while building something other than what you do for your day job (it can be easier to learn new things when not bogged down with old habits). This means that the simple service that should be humming along merrily with your name on it is the beginning of your adventures, rather than the end.

Here is a small roadmap to this basic service, so you can go about making it your own:

  • org.gameontext.sample.RoomImplementation This is class contains the core elements that make your microservice unique from others. Custom commands and items can be added here (via the org.gameontext.sample.RoomDescription member variable). The imaginatively named handleMessage method, in particular, is called when new messages arrive.

  • org.gameontext.sample.protocol.* This package contains a collection of classes that deal with the mechanics of the websocket connection that the game uses to allow players to interact with this service. RoomEndpoint is what it says: that is the WebSocket endpoint for the service.

  • org.gameontext.sample.rest.* This package defines a REST endpoint, with a single defined path: /health

  • src/main/liberty contains configuration for Liberty, a lightweight Java EE composable app server

  • src/test -- Yes! There are tests!

Things you might try:

  • Use RxJava to manage all of the connected WebSockets together as one event stream.
  • Call out to another API (NodeRed integration, Watson API, Weather API) to perform actions in the room.
  • Integrate this room with IFTTT, or Slack, or ...
  • .. other Advanced Adventures!

Remember our https://gameontext.org/#/terms. Most importantly, there are kids around: make your parents proud.

Running the app with hot-reload

Since this walkthrough is running on WebSphere Liberty we can set the app up for development without restarting the container.

First build the app with mvn clean install -P looseApp. This will create a gojava-1.0-SNAPSHOT.war.xml file in target/wlp/usr/server/gojava-room/apps rather than a packaged war. Now when you run mvn compile or if your IDE recompiles your code Liberty will pick up the change.

To run this in a Docker container we need to mount the classes directory, server directory and webapp directory as volumes so the container will pick up the changes without needing a rebuild.

Use the docker-compose.override.yml.example file as a guide and create a docker-compose.override.yml that mounts a volume with the files required by the war.xml file. The example override file also demonstrates how to add your container to the Game On Docker network so it can be accessed locally.

See the Advanced Adventure for local development with Docker for a more detailed walkthrough.

MicroProfile

MicroProfile is an open platform that optimizes the Enterprise Java for microservices architecture. In this application, we are using MicroProfile 1.3.

Features

  1. MicroProfile Metrics - This feature allows us to expose telemetry data. Using this, developers can monitor their services with the help of metrics.

The application uses the Timed, Counted and Metered metrics. To access these metrics, go to https://localhost:9443/metrics. The Metrics feature is configured with SSL and can only be accessed through https. You will need to login using the username and password configured in the server.xml. The default values are admin and password.

  1. MicroProfile Health Check - This feature helps us to determine the status of the service as well as its availability. This can be checked by accessing the /health endpoint.

How the build works

This project is built using Maven and makes use of the Liberty Maven plugin and the Cloud Foundry Maven plugin to integrate with Liberty and Bluemix.

Server feature definitions

For those of you familiar with the Liberty server configuration you will know that features are enabled in the server by adding a element to the server.xml. For this project the is provided by snippets from the Liberty app accelerator. This means that there is no element in the server.xml file. When the build is run these will appear in the server's configDropins/defaults directory.

Testing

You can write two types of tests: unit and integration tests. The unit tests will use the maven-surefire-plugin to run any tests found in packages that include "unit" in their name. The integration tests will:

  1. Start a Liberty server
  2. Use the maven-failsafe-plugin to run any tests that have packages that include "it" in their names
  3. Stop the Liberty server As integration tests are longer running they can be skipped by providing the skipTests flag: mvn install -DskipTests.

Code Coverage

The JaCoCo maven plugin is included in the build to generate code coverage reports. It will generate reports in multiple formats (HTML, XML, and CSV) in target/site/jacoco.

You can also access code reports on the web at codecov.io if your project is a public Github project built with Travis. The included travis.yml file includes a command to upload the code coverage reports automatically.

Build phases

The following shows what goals run at which phases in the default Maven lifecycle.

Phase Plugin Goal Profile Notes
initialize maven-dependency-plugin properties All Enables the copy of server snippets later on
initialize maven-enforcer-plugin enforce bluemix Makes sure the properties are set if deploying to Bluemix
initialize maven-antrun-plugin run bluemix Prints out what is going to be pushed
initialize maven-enforcer-plugin enforce existing-install Checks that if the liberty.install property is set that it points to an existing directory.
initialize jacoco-maven-plugin prepare-agent All Prepares a property pointing to the JaCoCo runtime agent for code coverage.
test maven-surefire-plugin test All
test jacoco-maven-plugin report All Creates a code coverage report.
prepare-package liberty-maven-plugin install-server All Creates the server using the server.xml in the src directory
package maven-war-plugin war All
package maven-dependency-plugin copy-server-files All Copies the server.xml snippets that contain the elements
package maven-resources-plugin copy-resources All Copies the WAR into the server
package liberty-maven-plugin package-server All Creates a ZIP or JAR (depending of if the runnable profile is enabled) containing the server and WAR
package cf-maven-plugin push bluemix Pushes the server up to bluemix
pre-integration-test liberty-maven-plugin start-server liberty-test Doesn't run when -DskipTests is set
integration-test maven-failsafe-plugin integration-test All
post-integration-test liberty-maven-plugin stop-server liberty-test Doesn't run when -DskipTests is set
verify maven-failsafe-plugin verify All
n/a liberty-maven-plugin n/a runnable Just sets properties to indicate that a runnable JAR should be made rather than a ZIP when packaging the server
n/a liberty-maven-plugin n/a downloadLiberty Just sets properties that are used in the install-server goal to installs the Liberty runtime. Doesn't run if liberty.install is set to an existing install of Liberty
n/a liberty-maven-plugin n/a existing-install Just sets properties that are used in the other Liberty goals to point to an existing Liberty install. Only runs if liberty.install is set to an existing install of Liberty