递归遍历生成树型结构

代码如下：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import com.alibaba.druid.support.json.JSONUtils;

public class 递归生成树 {

	public static void main(String[] args) {
		
		List<Map<String, Object>> list = getList();
		
		// 输出原始数据
		for (Map<String, Object> map : list) {
			System.out.println(map);
		}
		
		// 先拿出根节点
		List<Map<String, Object>> rootList = list.stream().filter(s -> s.get("parent_tree_id") == null).collect(Collectors.toList());
		
		// 把根节点和全部节点一起传进去递归去构造树
		diGui(rootList, list);
		
		// 转成json打印出来看看
		System.err.println(JSONUtils.toJSONString(rootList));
		// [{"tree_id":"1","tree_order":1,"tree_name":"配置采集","tree_level":1,"parent_tree_id":null,"child":[{"tree_id":"2","tree_order":1,"tree_name":"bbbbbb","tree_level":2,"parent_tree_id":"1","child":[]},{"tree_id":"3","tree_order":2,"tree_name":"都是","tree_level":2,"parent_tree_id":"1","child":[{"tree_id":"4","tree_order":1,"tree_name":"ttt","tree_level":3,"parent_tree_id":"3","child":[]}]}]},{"tree_id":"11","tree_order":2,"tree_name":"aaaaa","tree_level":1,"parent_tree_id":null,"child":[{"tree_id":"22","tree_order":1,"tree_name":"hahaha","tree_level":2,"parent_tree_id":"11","child":[]}]},{"tree_id":"111","tree_order":3,"tree_name":"ooooooooo","tree_level":1,"parent_tree_id":null,"child":[]}]
		// https://www.json.cn中去看结构
		
	}
	
	public static void diGui(List<Map<String, Object>> rootList, List<Map<String, Object>> allList) {
		
		for (Map<String, Object> m1 : rootList) {
			
			List<Map<String, Object>> childList = new ArrayList<>();
			
			for (Map<String, Object> m2 : allList) {
				if (toString(m1.get("tree_id")).equals(toString(m2.get("parent_tree_id")))) {
					childList.add(m2);
				}
			}
			m1.put("child", childList);
			if (childList.size() > 0) {
				diGui(childList, allList);
			}
		}
	}
	
	// 构造测试数据
	public static List<Map<String, Object>> getList() {
		
		List<Map<String, Object>> list = new ArrayList<>();
		
		// tree_id=主键，parent_tree_id父节点id
		Map<String, Object> m1 = new HashMap<>();
		m1.put("tree_id", "1");
		m1.put("tree_name", "配置采集");
		m1.put("tree_level", 1);
		m1.put("tree_order", 1);
		m1.put("parent_tree_id", null);
		
		Map<String, Object> m2 = new HashMap<>();
		m2.put("tree_id", "11");
		m2.put("tree_name", "aaaaa");
		m2.put("tree_level", 1);
		m2.put("tree_order", 2);
		m2.put("parent_tree_id", null);
		
		Map<String, Object> m3 = new HashMap<>();
		m3.put("tree_id", "2");
		m3.put("tree_name", "bbbbbb");
		m3.put("tree_level", 2);
		m3.put("tree_order", 1);
		m3.put("parent_tree_id", "1");
		
		Map<String, Object> m4 = new HashMap<>();
		m4.put("tree_id", "22");
		m4.put("tree_name", "hahaha");
		m4.put("tree_level", 2);
		m4.put("tree_order", 1);
		m4.put("parent_tree_id", "11");
		
		Map<String, Object> m5 = new HashMap<>();
		m5.put("tree_id", "3");
		m5.put("tree_name", "都是");
		m5.put("tree_level", 2);
		m5.put("tree_order", 2);
		m5.put("parent_tree_id", "1");
		
		Map<String, Object> m6 = new HashMap<>();
		m6.put("tree_id", "4");
		m6.put("tree_name", "ttt");
		m6.put("tree_level", 3);
		m6.put("tree_order", 1);
		m6.put("parent_tree_id", "3");
		
		Map<String, Object> m7 = new HashMap<>();
		m7.put("tree_id", "111");
		m7.put("tree_name", "ooooooooo");
		m7.put("tree_level", 1);
		m7.put("tree_order", 3);
		m7.put("parent_tree_id", null);

		list.add(m1);
		list.add(m2);
		list.add(m3);
		list.add(m4);
		list.add(m5);
		list.add(m6);
		list.add(m7);
		
		return list;
	}
	
	public static String toString(Object obj) {
		return obj == null || obj.toString().length() == 0 ? "" : obj.toString();
	}
}