[Java] java8 实现提取集合对象的每个属性

List<Bill> billList = new ArrayList<>();

List<String> goodsNameList = billList.stream().map(Bill::getGoodsName).collect(Collectors.toList());

MelotPageResult questionRelas = questionStudentRelaBiz.queryByParam(param);
List questionIds = questionRelas.getList().stream().map(QuestionStudentRela::getQuestionId).collect(Collectors.toList());

List students = new ArrayList();

List names =students.stream().map(Student::getName).collect(Collectors.toList())；