ConfigUtil (for Lists of any type)

ConfigUtil.java

import org.bukkit.configuration.ConfigurationSection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

public class ConfigUtil {

    /**
     * Retrieves a list from the given config section at the given path containing only elements of the given type.
     *
     * @param section The config section to get the list from.
     * @param path The path of the list within the given config section.
     * @param type The desired generic type of the list.
     * @return A list of all the objects of the give type at the given path within the given config section which could
     * be empty if the path does not represent a list or there are no objects of the given type in that list.
     */
    public static <T> List<T> getList(ConfigurationSection section, String path, Class<T> type) {
        List<?> wildList = section.getList(path, Collections.emptyList());
        return convertToTypedList(wildList, type);
    }

    /**
     * Retrieves a list from the given map with the given key containing only elements of the given type.
     *
     * @param serializedData The map that contains the desired list.
     * @param key The map key for the list.
     * @param type The desired generic type of the list.
     * @return A list of all the objects of the give type for the given key within the given map which could be empty
     * if none value for the key does not represent a list or there are no objects of the given type in that list.
     */
    public static <T> List<T> getList(Map<String, Object> serializedData, String key, Class<T> type) {
        Object o = serializedData.get(key);
        List<?> wildList;
        if (o instanceof List) {
            wildList = (List<?>) o;
        } else {
            wildList = Collections.emptyList();
        }
        return convertToTypedList(wildList, type);
    }

    // Helper method for the getList methods.
    private static <T> List<T> convertToTypedList(List<?> wildList, Class<T> type) {
        List<T> result = new ArrayList<>(wildList.size());
        for (Object o : wildList) {
            if (type.isInstance(o)) {
                result.add((T) o);
            }
        }
        return result;
    }

    // This is a singleton... you shouldn't be instantiating it.
    private ConfigUtil() {
        throw new AssertionError();
    }
}