普通list转树状list
public static List<User> list2tree(List<User> list) {
List<User> result = new ArrayList<>();
Map<Object, User> hash = list.stream().collect(Collectors.toMap(u -> u.getId(), u -> u));
for (User u : list) {
User p = hash.get(u.getParent());
if (p == null) {
result.add(u);
} else {
if (p.getChildren() == null) {
p.setChildren(new ArrayList<>());
}
p.getChildren().add(u);
}
}
return result;
}
树状list转普通list
public static List<User> tree2list(List<User> list) {
List<User> result = new ArrayList<>();
for (User u : list) {
List<User> c = u.getChildren();
result.add(u);
if (!CollectionUtils.isEmpty(c)) {
result.addAll(tree2list(c));
u.setChildren(null);//
}
}
return result;
}
list的其他应用：https://pingzhengguo.blog.csdn.net/article/details/86569380 (类型转换，排序，分组) https://pingzhengguo.blog.csdn.net/article/details/86540899(list的最大,最小,求和,平均) https://pingzhengguo.blog.csdn.net/article/details/86571528 (去重和提取重复元素) https://pingzhengguo.blog.csdn.net/article/details/88990352(list集合的分页问题)
