A simple Battlesnake written in Java.

This is a basic implementation of the Battlesnake API. It's a great starting point for anyone wanting to program their first Battlesnake using Java. It comes ready to use with Repl.it and provides instructions below for getting started. It can also be deployed to Heroku, or any other cloud provider you'd like.

Technologies

JDK 8
Maven
Heroku (optional)

Prerequisites

Battlesnake Account
Repl.it Account
GitHub Account and Git Command Line (optional)
Heroku Account and Heroku Command Line (optional)

Running Your Battlesnake on Repl.it

Login to your Repl.it account.
Click the 'Run on Repl.it' button above, or visit the following URL: https://repl.it/github/BattlesnakeOfficial/starter-snake-java.
You should see your Repl being initialized - this might take a few moments to complete.
Once your Repl is ready to run, click Run ▶️ at the top of the screen. You should see maven (and any other dependencies) being installed. Once installation is complete, your Battlesnake server will start and you should see the following:
```
[Thread-0] INFO org.eclipse.jetty.server.Server - Started @ms
```
Above the terminal window you'll see the live output from your Battlesnake server, including its URL. That URL will be the URL used to create your Battlesnake in the next step. If you visit that URL in your browser, you should see text similar to this:
```
{"apiversion": "1", "author": "", "color": "#888888", "head": "default", "tail": "default"}
```

This means your Battlesnake is running correctly on Repl.it.

At this point your Battlesnake is live and ready to enter games!

Customizing Your Battlesnake

Now you're ready to start customizing your Battlesnake's appearance and behavior.

Changing Appearance

Locate the index method inside Snake.java. You should see code that looks like this:

Map<String, String> response = new HashMap<>();
response.put("apiversion", "1");
response.put("author", "");           // TODO: Your Battlesnake Username
response.put("color", "#888888");     // TODO: Personalize
response.put("head", "default");  // TODO: Personalize
response.put("tail", "default");  // TODO: Personalize
return response;

This function is called by the game engine periodically to make sure your Battlesnake is healthy, responding correctly, and to determine how your Battlesnake will appear on the game board. See Battlesnake Personalization for how to customize your Battlesnake's appearance using these values.

Whenever you update these values, you can refresh your Battlesnake on your profile page to use your latest configuration. Your changes should be reflected in the UI, as well as any new games created.

Changing Behavior

On every turn of each game your Battlesnake receives information about the game board and must decide its next move.

Locate the move method inside Snake.java. You should see code that looks like this:

public Map<String, String> move(JsonNode moveRequest) {

    String[] possibleMoves = { "up", "down", "left", "right" };

    // Choose a random direction to move in
    int choice = new Random().nextInt(possibleMoves.length);
    String move = possibleMoves[choice];

    LOG.info("MOVE {}", move);

    Map<String, String> response = new HashMap<>();
    response.put("move", move);
    return response;
}

Possible moves are "up", "down", "left", or "right". To start your Battlesnake will choose a move randomly. Your goal as a developer is to read information sent to you about the board (available in the moveRequest variable) and make an intelligent decision about where your Battlesnake should move next.

See the Battlesnake Rules for more information on playing the game, moving around the board, and improving your algorithm.

Updating Your Battlesnake

After making changes to your Battlesnake, you can restart your Repl to have the change take effect (or in many cases your Repl will restart automatically).

Once the Repl has restarted you can create a new game with your Battlesnake to watch your latest changes in action.

At this point you should feel comfortable making changes to your code and starting new Battlesnake games to test those changes!

Developing Your Battlesnake Further

Now you have everything you need to start making your Battlesnake super smart! Here are a few more helpful tips:

Keeping your Repl open in a second window while games are running is helpful for watching server activity and debugging any problems with your Battlesnake.
The projected is configured with a logger that you can use the code LOG.info() to output information to your server logs. This is very useful for debugging logic in your code during Battlesnake games.

Review the Battlesnake API Docs to learn what information is provided with each command. You can also output the data to your logs:

    public Map<String, String> move(JsonNode moveRequest) {
        try {
            LOG.info("Data: {}", JSON_MAPPER.writerWithDefaultPrettyPrinter().writeValueAsString(moveRequest));
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }

        String[] possibleMoves = { "up", "down", "left", "right" };

        // Choose a random direction to move in
        int choice = new Random().nextInt(possibleMoves.length);
        String move = possibleMoves[choice];

        LOG.info("MOVE {}", move);

        Map<String, String> response = new HashMap<>();
        response.put("move", move);
        return response;
    }

When viewing a Battlesnake game you can pause playback and step forward/backward one frame at a time. If you review your logs at the same time, you can see what decision your Battlesnake made on each turn.

Joining a Battlesnake Arena

Once you've made your Battlesnake behave and survive on its own, you can enter it into the Global Battlesnake Arena to see how it performs against other Battlesnakes worldwide.

Arenas will regularly create new games and rank Battlesnakes based on their results. They're a good way to get regular feedback on how well your Battlesnake is performing, and a fun way to track your progress as you develop your algorithm.

(Optional) Deploying Your First Battlesnake with Heroku

Fork this repo into your GitHub Account.

Clone your forked repo into your local environment.

git clone git@github.com:[YOUR-GITHUB-USERNAME]/starter-snake-java.git

Create a new Heroku app to run your Battlesnake.
```
heroku create [YOUR-APP-NAME]
```
Deploy your Battlesnake code to Heroku.
```
git push heroku master
```
Open your new Heroku app in your browser.
```
heroku open
```
If everything was successful, you should see the following text:
```
{"tailType":"default","color":"#888888","headType":"default","author":"","apiversion":"1"}
```
Optionally, you can view your server logs using the Heroku logs command heroku logs --tail. The --tail option will show a live feed of your logs in real-time.

At this point your Battlesnake is live and ready to enter games!

(Optional) Updating Your Battlesnake with Heroku

After making changes, commit them using git and deploy your changes to Heroku.

git add .
git commit -m "update my battlesnake's appearance"
git push heroku master

Once Heroku has updated you can create a new game with your Battlesnake to view your latest changes in action.

At this point you should feel comfortable making changes to your code and deploying those changes to Heroku!

(Optional) Using a Cloud Provider

As your Battlesnake gets more complex, it might make sense to move it to a dedicated hosting provider such as GCP or AWS. We suggest choosing a platform you're familiar with, or one you'd be interested in learning more about.

If you have questions or ideas, our developer community on Slack and Discord will be able to help out.

(Optional) Running Your Battlesnake Locally

Eventually you might want to run your Battlesnake server locally for faster testing and debugging. You can do this by installing both JDK 8 and Maven, then running:

mvn compile exec:exec

This will start the Battlesnake server on port 8080.

Note: You cannot create games on play.battlesnake.com using a locally running Battlesnake unless you install and use a port forwarding tool like ngrok.

(Optional) Running Unit Tests

The starter snake is setup with the JUnit Jupiter testing framework, if you are interested in developing unit tests for your Battlesnake. You can find the test cases in SnakeTest.java

Run the following to start the tests:

mvn compile test

Questions?

All documentation is available at docs.battlesnake.com, including detailed Guides, API References, and Tips.

You can also join the Battlesnake Developer Community on Slack and Discord. We have a growing community of Battlesnake developers of all skill levels wanting to help everyone succeed and have fun with Battlesnake :)

arit007/starter-snake-java