jdk8 相关

6.1获取map集合报空指针解决

list.stream().collect(Collectors.toMap(x->x.getId(),y->ObjectUtil.isEmpty(y.getUserAccount())?"":y.getUserAccount()));

6.2map中key相同解决

当key值相同时取第一个value值或者第二个value值

Map<Long,String>map=userList.stream() .collect(Collectors.toMap(User::getId, User::getUsername, (v1, v2) -> v1));