Java使用stream来把list集合转化为树形结构（一行解决超简单递归）
一、前言
我们在日常开发中，必不可少的就是树形结构。有的时候可以使用mybatis的resultMap进行转化，有的时候需要进行Java进行手动转化为树结构。今天和大家分析一个JDK8新特性Stream来实现list到树形结构的转化！
二、创建返回前端的实体类VO
import lombok.Data; import java.util.List; /** * @author wangzhenjun * @date 2022/2/28 10:28 */ @Data public class NodeVO { private String id; private String name; private String pid; private List<NodeVO> children; public NodeVO(String id, String name, String pid) { this.id = id; this.name = name; this.pid = pid; } }
三、list转树形方法
public static List<NodeVO> streamToTree(List<NodeVO> treeList, String parentId) { List<NodeVO> list = treeList.stream() // 过滤父节点 .filter(parent -> parent.getPid().equals(parentId)) // 把父节点children递归赋值成为子节点 .map(child -> { child.setChildren(streamToTree(treeList,child.getId())); return child; }).collect(Collectors.toList()); return list; }
四、测试
public static void main(String[] args) { NodeVO NodeVO1 = new NodeVO("1","山东省","0"); NodeVO NodeVO2 = new NodeVO("2","青岛市","1"); NodeVO NodeVO3 = new NodeVO("3","市北区","2"); NodeVO NodeVO4 = new NodeVO("4","济南市","1"); NodeVO NodeVO5 = new NodeVO("5","浙江省","0"); NodeVO NodeVO6 = new NodeVO("6","杭州市","5"); NodeVO NodeVO7 = new NodeVO("7","西湖区","6"); List<NodeVO> list = new ArrayList<>(); list.add(NodeVO1); list.add(NodeVO2); list.add(NodeVO3); list.add(NodeVO4); list.add(NodeVO5); list.add(NodeVO6); list.add(NodeVO7); // 默认父节点id为0 List<NodeVO> nodeVOList = streamToTree(list,"0"); System.out.println(JSON.toJSONString(nodeVOList)); }
结果展示：
[ { "children": [ { "children": [ { "children": [], "id": "3", "name": "市北区", "pid": "2" } ], "id": "2", "name": "青岛市", "pid": "1" }, { "children": [], "id": "4", "name": "济南市", "pid": "1" } ], "id": "1", "name": "山东省", "pid": "0" }, { "children": [ { "children": [ { "children": [], "id": "7", "name": "西湖区", "pid": "6" } ], "id": "6", "name": "杭州市", "pid": "5" } ], "id": "5", "name": "浙江省", "pid": "0" } ]
五、总结
也可以使用两个for来实现，小编还是觉得Stream比较优雅哈，哈哈哈！！如果对你有用点个赞呗！
