Optional.ofNullable()方法

public static void main(String[] args) {
        List<String> list = null;
        list.forEach(x -> System.out.println(x));
    }

public static void main(String[] args) {
        List<String> list = null;
        List<String> newList = Optional.ofNullable(list).orElse(Lists.newArrayList());
        newList.forEach(x -> System.out.println(x));
    }