Add example usage for configs to the MDK (#9596)

Demonstrates proper usage of different config value types, validation, transformation/parsing, load/reload handling and direct field access.

src/main/java/com/example/examplemod/Config.java

@@ -0,0 +1,64 @@
+package com.example.examplemod;
+
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Item;
+import net.minecraftforge.common.ForgeConfigSpec;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.event.config.ModConfigEvent;
+import net.minecraftforge.registries.ForgeRegistries;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+// An example config class. This is not required, but it's a good idea to have one to keep your config organized.
+// Demonstrates how to use Forge's config APIs
+@Mod.EventBusSubscriber(modid = ExampleMod.MODID, bus = Mod.EventBusSubscriber.Bus.MOD)
+public class Config
+{
+    private static final ForgeConfigSpec.Builder BUILDER = new ForgeConfigSpec.Builder();
+
+    private static final ForgeConfigSpec.BooleanValue LOG_DIRT_BLOCK = BUILDER
+            .comment("Whether to log the dirt block on common setup")
+            .define("logDirtBlock", true);
+
+    private static final ForgeConfigSpec.IntValue MAGIC_NUMBER = BUILDER
+            .comment("A magic number")
+            .defineInRange("magicNumber", 42, 0, Integer.MAX_VALUE);
+
+    public static final ForgeConfigSpec.ConfigValue<String> MAGIC_NUMBER_INTRODUCTION = BUILDER
+            .comment("What you want the introduction message to be for the magic number")
+            .define("magicNumberIntroduction", "The magic number is... ");
+
+    // a list of strings that are treated as resource locations for items
+    private static final ForgeConfigSpec.ConfigValue<List<? extends String>> ITEM_STRINGS = BUILDER
+            .comment("A list of items to log on common setup.")
+            .defineListAllowEmpty(Collections.singletonList("items"), () -> List.of("minecraft:iron_ingot"), Config::validateItemName);
+
+    static final ForgeConfigSpec SPEC = BUILDER.build();
+
+    public static boolean logDirtBlock;
+    public static int magicNumber;
+    public static String magicNumberIntroduction;
+    public static Set<Item> items;
+
+    private static boolean validateItemName(final Object obj)
+    {
+        return obj instanceof final String itemName && ForgeRegistries.ITEMS.containsKey(new ResourceLocation(itemName));
+    }
+
+    @SubscribeEvent
+    static void onLoad(final ModConfigEvent event)
+    {
+        logDirtBlock = LOG_DIRT_BLOCK.get();
+        magicNumber = MAGIC_NUMBER.get();
+        magicNumberIntroduction = MAGIC_NUMBER_INTRODUCTION.get();
+
+        // convert the list of strings into a set of items
+        items = ITEM_STRINGS.get().stream()
+                .map(itemName -> ForgeRegistries.ITEMS.getValue(new ResourceLocation(itemName)))
+                .collect(Collectors.toSet());
+    }
+}

src/main/java/com/example/examplemod/ExampleMod.java

@@ -18,7 +18,9 @@ import net.minecraftforge.event.BuildCreativeModeTabContentsEvent;
 import net.minecraftforge.event.server.ServerStartingEvent;
 import net.minecraftforge.eventbus.api.IEventBus;
 import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.ModLoadingContext;
 import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.config.ModConfig;
 import net.minecraftforge.fml.event.lifecycle.FMLClientSetupEvent;
 import net.minecraftforge.fml.event.lifecycle.FMLCommonSetupEvent;
 import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
@@ -78,13 +80,22 @@ public class ExampleMod
 
         // Register the item to a creative tab
         modEventBus.addListener(this::addCreative);
+
+        // Register our mod's ForgeConfigSpec so that Forge can create and load the config file for us
+        ModLoadingContext.get().registerConfig(ModConfig.Type.COMMON, Config.SPEC);
     }
 
     private void commonSetup(final FMLCommonSetupEvent event)
     {
         // Some common setup code
         LOGGER.info("HELLO FROM COMMON SETUP");
+
+        if (Config.logDirtBlock)
             LOGGER.info("DIRT BLOCK >> {}", ForgeRegistries.BLOCKS.getKey(Blocks.DIRT));
+
+        LOGGER.info(Config.magicNumberIntroduction + Config.magicNumber);
+
+        Config.items.forEach((item) -> LOGGER.info("ITEM >> {}", item.toString()));
     }
 
     // Add the example block item to the building blocks tab