jMonkeyEngine-wiki/docs/modules/networking/pages/headless_server.adoc

= jME3 Headless Server
:revnumber: 2.0
:revdate: 2020/07/24
:keywords: server, spidermonkey, headless, network, documentation


When adding multiplayer to your game, you may find that your server needs to know about game state (e.g. where are players, objects? Was that a direct hit? etc.) You can code all this up yourself, but there's an easier way.

It's very easy to change your current (client) game to function as a server as well.


== What Does Headless Mean?

A headless server…

*  does not display any output – no window opens, no audio plays, no graphics are rendered.
*  ignores all input – no input handling.
*  keeps game state – you can attach to, transform, and save the rootNode, although the scene is not displayed.
*  calls the `simpleUpdate()` loop – you can run tests and trigger events as usual.


== Client Code

First, let's take a look at the default way of creating a new game (in its simplest form):

[source,java]
----

public static void main(String[] args) {
  Application app = new Main();
  app.start();
}
----


== Headless Server Code

Now, with a simple change you can start your game in Headless mode. This means that all input and audio/visual output will be ignored. That's a good thing for a server.

[source,java]
----

import com.jme3.system.JmeContext;
import com.jme3.system.JmeContext.Type;

public static void main(String[] args) {
  Application app = new Main();
  app.start(JmeContext.Type.Headless);
}
----


== Next steps

Okay, so you can now start your game in a headless "`server mode`", where to go from here?

*  Parse `String[] args` from the `main`-method to enable server mode on demand (e.g. start your server like `java -jar mygame.jar –server`.
*  Integrate xref:networking.adoc[SpiderMonkey], to provide game updates to the server over a network.
*  Only execute code that's needed. (E.g. place all rendering code inside an `if (servermode)`-block) (or `if (!servermode)` for the client).
*  Add decent xref:tutorials:how-to/java/logging.adoc[logging] so your server actually makes sense.