public class Node { private int id; private int pid; private String name; private List<Node> sub = new ArrayList<>(); public Node(int id, int pid) { this.id = id; this.pid = pid; } public Node(int id, int pid, String name) { this(id, pid); this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } public int getPid() { return pid; } public void setPid(int pid) { this.pid = pid; } public String getName() { return name; } public void setName(String name) { this.name = name; } public List<Node> getSub() { return sub; } public void setSub(List<Node> sub) { this.sub = sub; } }
public class TreeUtil { public static List<Node> buildTree(List<Node> nodes) { Map<Integer, List<Node>> sub = nodes.stream().filter(node -> node.getPid() != 0).collect(Collectors.groupingBy(node -> node.getPid())); nodes.forEach(node -> node.setSub(sub.get(node.getId()))); return nodes.stream().filter(node -> node.getPid() == 0).collect(Collectors.toList()); } }
public class Main { public static void main(String[] args) { Node dennis = new Node(1, 0, "dennis"); Node calm = new Node(2, 0, "calm"); Node daughter = new Node(3, 1, "daughter"); Node grandson = new Node(4, 3, "grandson"); Node son = new Node(5, 2, "son"); List<Node> nodes = Lists.newArrayList(dennis, calm, daughter, son, grandson); List<Node> tree = TreeUtil.buildTree(nodes); System.out.println(JSON.toJSONString(tree)); } }
