泛型ArrayList转数组

@SuppressWarnings("unchecked")
public static <T> T[] toArray(Class<?> cls, ArrayList<T> items) {
    if (items == null || items.size() == 0) {
        return (T[]) Array.newInstance(cls, 0);
    }
    return items.toArray((T[]) Array.newInstance(cls, items.size()));
}