Minestom/demo/src/main/java/net/minestom/demo/MainDemo.java

package net.minestom.demo;

import net.minestom.server.MinecraftServer;
import net.minestom.server.coordinate.Pos;
import net.minestom.server.entity.Player;
import net.minestom.server.event.GlobalEventHandler;
import net.minestom.server.event.player.PlayerLoginEvent;
import net.minestom.server.instance.*;
import net.minestom.server.instance.batch.ChunkBatch;
import net.minestom.server.instance.block.Block;
import org.jetbrains.annotations.NotNull;

import java.util.List;

public class MainDemo {

    public static void main(String[] args) {
        // Initialization
        MinecraftServer minecraftServer = MinecraftServer.init();

        InstanceManager instanceManager = MinecraftServer.getInstanceManager();
        // Create the instance
        InstanceContainer instanceContainer = instanceManager.createInstanceContainer();
        // Set the ChunkGenerator
        instanceContainer.setChunkGenerator(new GeneratorDemo());

        // Add an event callback to specify the spawning instance (and the spawn position)
        GlobalEventHandler globalEventHandler = MinecraftServer.getGlobalEventHandler();
        globalEventHandler.addListener(PlayerLoginEvent.class, event -> {
            final Player player = event.getPlayer();
            event.setSpawningInstance(instanceContainer);
            player.setRespawnPoint(new Pos(0, 42, 0));
        });

        // Start the server on port 25565
        minecraftServer.start("0.0.0.0", 25565);
    }

    private static class GeneratorDemo implements ChunkGenerator {

        @Override
        public void generateChunkData(@NotNull ChunkBatch batch, int chunkX, int chunkZ) {
            // Set chunk blocks
            for (byte x = 0; x < Chunk.CHUNK_SIZE_X; x++)
                for (byte z = 0; z < Chunk.CHUNK_SIZE_Z; z++) {
                    for (byte y = 0; y < 40; y++) {
                        batch.setBlock(x, y, z, Block.STONE);
                    }
                }
        }

        @Override
        public List<ChunkPopulator> getPopulators() {
            return null;
        }
    }

}