Merge pull request #3692 from huangxin8899/v5-dev

增加函数式构建树的方法（无需继承特定Tree类）

hutool-core/src/main/java/cn/hutool/core/lang/tree/TreeUtil.java

@@ -5,9 +5,10 @@ import cn.hutool.core.lang.tree.parser.DefaultNodeParser;
 import cn.hutool.core.lang.tree.parser.NodeParser;
 import cn.hutool.core.util.ObjectUtil;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
+import java.util.function.BiConsumer;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 /**
  * 树工具类
@@ -277,4 +278,52 @@ public class TreeUtil {
 	public static <E> Tree<E> createEmptyNode(E id) {
 		return new Tree<E>().setId(id);
 	}
+
+	/**
+	 * 函数式构建树状结构(无需继承Tree类)
+	 *
+	 * @param nodes			需要构建树集合
+	 * @param rootId		根节点ID
+	 * @param idFunc		获取节点ID函数
+	 * @param parentIdFunc	获取节点父ID函数
+	 * @param setChildFunc	设置孩子集合函数
+	 * @param <T>			节点ID类型
+	 * @param <E>			节点类型
+	 * @return List
+	 */
+	public static <T, E> List<E> build(List<E> nodes, T rootId, Function<E, T> idFunc, Function<E, T> parentIdFunc, BiConsumer<E, List<E>> setChildFunc) {
+		List<E> rootList = nodes.stream().filter(tree -> parentIdFunc.apply(tree).equals(rootId)).collect(Collectors.toList());
+		Map<T, T> filterOperated = new HashMap<>(rootList.size() + nodes.size());
+		//对每个根节点都封装它的孩子节点
+		rootList.forEach(root -> setChildren(root, nodes, filterOperated, idFunc, parentIdFunc, setChildFunc));
+		return rootList;
+	}
+
+	/**
+	 * 封装孩子节点
+	 *
+	 * @param root				根节点
+	 * @param nodes				节点集合
+	 * @param filterOperated	过滤操作Map
+	 * @param idFunc			获取节点ID函数
+	 * @param parentIdFunc		获取节点父ID函数
+	 * @param setChildFunc		设置孩子集合函数
+	 * @param <T>				节点ID类型
+	 * @param <E>				节点类型
+	 */
+	private static <T, E> void setChildren(E root, List<E> nodes, Map<T, T> filterOperated, Function<E, T> idFunc, Function<E, T> parentIdFunc, BiConsumer<E, List<E>> setChildFunc) {
+		List<E> children = new ArrayList<>();
+		nodes.stream()
+			//过滤出未操作过的节点
+			.filter(body -> !filterOperated.containsKey(idFunc.apply(body)))
+			//过滤出孩子节点
+			.filter(body -> Objects.equals(idFunc.apply(root), parentIdFunc.apply(body)))
+			.forEach(body -> {
+				filterOperated.put(idFunc.apply(body), idFunc.apply(root));
+				children.add(body);
+				//递归 对每个孩子节点执行同样操作
+				setChildren(body, nodes, filterOperated, idFunc, parentIdFunc, setChildFunc);
+			});
+		setChildFunc.accept(root, children);
+	}
 }

hutool-core/src/test/java/cn/hutool/core/lang/tree/TreeTest.java

@@ -1,6 +1,7 @@
 package cn.hutool.core.lang.tree;
 
 import cn.hutool.core.collection.CollUtil;
+import lombok.Data;
 import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
@@ -122,4 +123,39 @@ public class TreeTest {
 		tree.walk((tr) -> ids2.add(tr.getId()));
 		assertEquals(7, ids2.size());
 	}
+
+
+	@Data
+	static class Area {
+		private Integer id;
+		private String name;
+		private Integer parentId;
+		private List<Area> childrenList;
+
+		public Area(Integer id, String name, Integer parentId) {
+			this.id = id;
+			this.name = name;
+			this.parentId = parentId;
+		}
+	}
+	// 模拟数据
+	static List<Area> areaList = CollUtil.newArrayList();
+	static {
+		areaList.add(new Area(1, "中国", 0));
+		areaList.add(new Area(2, "北京", 1));
+		areaList.add(new Area(3, "上海", 1));
+		areaList.add(new Area(4, "广东", 1));
+		areaList.add(new Area(5, "广州", 4));
+		areaList.add(new Area(6, "深圳", 4));
+		areaList.add(new Area(7, "浙江", 1));
+		areaList.add(new Area(8, "杭州", 7));
+	}
+
+	@Test
+	public void builderTest() {
+		List<Area> list = TreeUtil.build(areaList, 0, Area::getId, Area::getParentId, Area::setChildrenList);
+		final Area root = list.get(0);
+		final Integer parentId = root.getChildrenList().get(0).getParentId();
+		assertEquals(root.getId(), parentId);
+	}
 }