plugin-loader

plugin-loader is a simple system mods can use to detect and load plugin implementations from within other mod jars.

Creating a loader

Loaders are a soft-dependency. If plugin-loader is not installed, the mod should still load fine, it just won't load plugins.

Loader Builder Detection

Create a pluginloader.json file inside the root of your resources directory with the following contents:

{
  "id": "modid",
  "initializer": "com.website.foo.MyLoaderCreator"
}

• id is your modid.
• initializer points to a class that implements LoaderCreator.

plugin-loader looks for this JSON file and uses it to discover if you have a loader, and where it is.

Loader Creation

Create a class at the location you pointed at in your JSON and implement LoaderCreator. Use the PluginLoaderBuilder to create a new PluginLoader instance. An extreme barebones example would look like this:

public class MyLoader implements LoaderCreator {
    
    public void createLoaders() {
        new PluginLoaderBuilder("modid").build();
    }
}

To have more control over the behavior, you can use some of the other methods:

public class MyLoader implements LoaderCreator {
    
    public void createLoaders() {
        new PluginLoaderBuilder("some_id")
                .withValidator(ValidationStrategy.instanceOf(Runnable.class))
                .withInitializer((aClass, container) -> {
                    try {
                        aClass.newInstance();
                    } catch (IllegalAccessException | InstantiationException e) {
                        e.printStackTrace();
                    }
                })
                .build();
    }
}

See the javadoc for more information.

Creating a Plugin

Plugin implementation is very simple. Create a plugins directory in the root of your resources directory. In there, create a JSON file named modid.plugin.json, where modid is the ID of the mod you want to be loaded by. The JSON file should be structured like so:

{
  "id": "my_plugin",
  "initializer": "com.website.foo.MyPlugin",
  "data": {
    "foo": "bar"
  }
}

• id is the unique ID of your plugin.
• initializer points to a your plugin class.
• data is an optional field that depends on the mod's implementation. It is passed as a raw JsonObject to the loader.

After this, everything is left up to the loader, so see their docs to know what other requirements are needed.