public class TestPlugin extends JavaPlugin implements Listener {

    @Override
    public void onEnable() {
        getLogger().info("Test plugin loaded");
        Bukkit.getPluginManager().registerEvents(this, this);
    }

    @EventHandler(priority = EventPriority.LOW, ignoreCancelled = true)
    public void onCreatureSpawn(final CreatureSpawnEvent e) {
        e.setCancelled(true);
        getLogger().info(e.getSpawnReason().toString());
    }
}