Stream List＜List＜Object＞＞ 转 List＜Object＞

Stream List＜List＜Object＞＞ 转 List＜Object＞

List collect = authors.stream().map(Author::getBookList).flatMap(Collection::stream).collect(Collectors.toList());

List collect1 = authors.stream().map(Author::getBookList).flatMap(author-> author.stream()).collect(Collectors.toList());