Basic plugin manager

src/main/java/emu/grasscutter/Config.java

 package emu.grasscutter;
 
-import java.util.ArrayList;
-
 public final class Config {
 
 	public String DatabaseUrl = "mongodb://localhost:27017";
@@ -12,6 +10,7 @@ public final class Config {
 	public String PACKETS_FOLDER = "./packets/";
 	public String DUMPS_FOLDER = "./dumps/";
 	public String KEY_FOLDER = "./keys/";
+	public String PLUGINS_FOLDER = "./plugins/";
 
 	public String RunMode = "HYBRID"; // HYBRID, DISPATCH_ONLY, GAME_ONLY
 	public GameServerOptions GameServer = new GameServerOptions();

src/main/java/emu/grasscutter/Grasscutter.java

@@ -8,6 +8,7 @@ import java.io.InputStreamReader;
 import java.net.InetSocketAddress;
 
 import emu.grasscutter.command.CommandMap;
+import emu.grasscutter.plugin.PluginManager;
 import emu.grasscutter.utils.Utils;
 import org.reflections.Reflections;
 import org.slf4j.LoggerFactory;
@@ -35,6 +36,7 @@ public final class Grasscutter {
 	private static GameServer gameServer;
 	
 	public static final Reflections reflector = new Reflections();
+	public static final PluginManager pluginManager;
 	
 	static {
 		// Declare logback configuration.
@@ -45,6 +47,9 @@ public final class Grasscutter {
 		
 		// Check server structure.
 		Utils.startupCheck();
+		
+		// Call plugin manager.
+		pluginManager = new PluginManager();
 	}
 	
     public static void main(String[] args) throws Exception {
@@ -91,8 +96,6 @@ public final class Grasscutter {
 			getLogger().error("Shutting down...");
 			System.exit(1);
 		}
-
-
 		
 		// Open console.
 		startConsole();
@@ -161,4 +164,8 @@ public final class Grasscutter {
 	public static GameServer getGameServer() {
 		return gameServer;
 	}
+	
+	public static PluginManager getPluginManager() {
+		return pluginManager;
+	}
 }

src/main/java/emu/grasscutter/plugin/Plugin.java

+package emu.grasscutter.plugin;
+
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.server.game.GameServer;
+
+/**
+ * The base class for all plugins to extend.
+ */
+public abstract class Plugin {
+    private final PluginIdentifier identifier;
+
+    /**
+     * Empty constructor for developers.
+     * Should not be called by users.
+     */
+    public Plugin() {
+        this(new PluginIdentifier("", "", "", new String[]{}));
+    }
+    
+    /**
+     * Constructor for plugins.
+     * @param identifier The plugin's identifier.
+     */
+    public Plugin(PluginIdentifier identifier) {
+        this.identifier = identifier;
+    }
+
+    /**
+     * The plugin's identifier instance.
+     * @return An instance of {@link PluginIdentifier}.
+     */
+    public final PluginIdentifier getIdentifier(){
+        return this.identifier;
+    }
+
+    /**
+     * Get the plugin's name.
+     */
+    public final String getName() {
+        return this.identifier.name;
+    }
+
+    /**
+     * Get the plugin's description.
+     */
+    public final String getDescription() {
+        return this.identifier.description;
+    }
+
+    /**
+     * Get the plugin's version.
+     */
+    public final String getVersion() {
+        return this.identifier.version;
+    }
+
+    /**
+     * Returns the server that initialized the plugin.
+     * @return A server instance.
+     */
+    public final GameServer getServer() {
+        return Grasscutter.getGameServer();
+    }
+    
+    /* Called when the plugin is first loaded. */
+    public void onLoad() { }
+    /* Called after (most of) the server enables. */
+    public void onEnable() { }
+    /* Called before the server disables. */
+    public void onDisable() { }
+}

src/main/java/emu/grasscutter/plugin/PluginConfig.java

+package emu.grasscutter.plugin;
+
+/**
+ * The data contained in the plugin's `plugin.json` file.
+ */
+public final class PluginConfig {
+    public String name, description, version;
+    public String mainClass;
+    public String[] authors;
+
+    /**
+     * Attempts to validate this config instance.
+     * @return True if the config is valid, false otherwise.
+     */
+    public boolean validate() {
+        return name != null && description != null && mainClass != null;
+    }
+}

src/main/java/emu/grasscutter/plugin/PluginIdentifier.java

+package emu.grasscutter.plugin;
+
+// TODO: Potentially replace with Lombok?
+public final class PluginIdentifier {
+    public final String name, description, version;
+    public final String[] authors;
+    
+    public PluginIdentifier(
+            String name, String description, String version,
+            String[] authors
+    ) {
+        this.name = name;
+        this.description = description;
+        this.version = version;
+        this.authors = authors;
+    }
+
+    /**
+     * Converts a {@link PluginConfig} into a {@link PluginIdentifier}.
+     */
+    public static PluginIdentifier fromPluginConfig(PluginConfig config) {
+        if(!config.validate())
+            throw new IllegalArgumentException("A valid plugin config is required to convert into a plugin identifier.");
+        return new PluginIdentifier(
+                config.name, config.description, config.version,
+                config.authors
+        );
+    }
+}

src/main/java/emu/grasscutter/plugin/PluginManager.java

+package emu.grasscutter.plugin;
+
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.utils.Utils;
+
+import java.io.File;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Manages the server's plugins & the event system.
+ */
+public final class PluginManager {
+    private final Map<String, Plugin> plugins = new HashMap<>();
+    
+    public PluginManager() {
+        this.loadPlugins(); // Load all plugins from the plugins directory.
+    }
+
+    /**
+     * Loads plugins from the config-specified directory.
+     */
+    private void loadPlugins() {
+        String directory = Grasscutter.getConfig().PLUGINS_FOLDER;
+        File pluginsDir = new File(Utils.toFilePath(directory));
+        if(!pluginsDir.exists() && !pluginsDir.mkdirs()) {
+            Grasscutter.getLogger().error("Failed to create plugins directory: " + pluginsDir.getAbsolutePath());
+            return;
+        }
+        
+        File[] files = pluginsDir.listFiles();
+        if(files == null) {
+            // The directory is empty, there aren't any plugins to load.
+            return;
+        }
+        
+        List<File> plugins = Arrays.stream(files)
+                .filter(file -> file.getName().endsWith(".jar"))
+                .collect(Collectors.toList());
+        
+        plugins.forEach(plugin -> {
+            try {
+                URL url = plugin.toURI().toURL();
+                try (URLClassLoader loader = new URLClassLoader(new URL[]{url})) {
+                    URL configFile = loader.findResource("plugin.json");
+                    InputStreamReader fileReader = new InputStreamReader(configFile.openStream());
+                    
+                    PluginConfig pluginConfig = Grasscutter.getGsonFactory().fromJson(fileReader, PluginConfig.class);
+                    if(!pluginConfig.validate()) {
+                        Utils.logObject(pluginConfig);
+                        Grasscutter.getLogger().warn("Plugin " + plugin.getName() + " has an invalid config file.");
+                        return;
+                    }
+                    
+                    Class<?> pluginClass = loader.loadClass(pluginConfig.mainClass);
+                    Plugin pluginInstance = (Plugin) pluginClass.getDeclaredConstructor(PluginIdentifier.class)
+                            .newInstance(PluginIdentifier.fromPluginConfig(pluginConfig));
+                    this.loadPlugin(pluginInstance);
+                    
+                    fileReader.close(); // Close the file reader.
+                } catch (ClassNotFoundException ignored) {
+                    Grasscutter.getLogger().warn("Plugin " + plugin.getName() + " has an invalid main class.");
+                }
+            } catch (Exception exception) {
+                Grasscutter.getLogger().error("Failed to load plugin: " + plugin.getName(), exception);
+            }
+        });
+    }
+
+    /**
+     * Load the specified plugin.
+     * @param plugin The plugin instance.
+     */
+    private void loadPlugin(Plugin plugin) {
+        Grasscutter.getLogger().info("Loading plugin: " + plugin.getName());
+        
+        // Add the plugin to the list of loaded plugins.
+        this.plugins.put(plugin.getName(), plugin);
+        // Call the plugin's onLoad method.
+        plugin.onLoad();
+    }
+
+    /**
+     * Enables all registered plugins.
+     */
+    public void enablePlugins() {
+        
+    }
+    
+    /**
+     * Disables all registered plugins.
+     */
+    public void disablePlugins() {
+        
+    }
+}
\ No newline at end of file

src/main/java/emu/grasscutter/utils/Utils.java

@@ -137,6 +137,15 @@ public final class Utils {
 		return nonNull != null ? nonNull : fallback;
 	}
 
+	/**
+	 * Logs an object to the console.
+	 * @param object The object to log.
+	 */
+	public static void logObject(Object object) {
+		String asJson = Grasscutter.getGsonFactory().toJson(object);
+		Grasscutter.getLogger().info(asJson);
+	}
+	
 	/**
 	 * Checks for required files and folders before startup.
 	 */