【Java 开发实例】Java8 List 转树结构

废话不多说系列，直接上代码。（一切看代码！）

一、完整代码示例

（1）创建 VO 实体类

import lombok.Data; // Lombok 注解
import java.util.List;

@Data
public class NodeVO {
    private String id;
    private String name;
    private String pid; // 上级ID
    private List<NodeVO> children; // 子节点集合

    public NodeVO(String id, String name, String pid) {
        this.id = id;
        this.name = name;
        this.pid = pid;
    }
}

（2）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;
}

（3）测试示例

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 = Arrays.asList(NodeVO1, NodeVO2, NodeVO3, NodeVO4, NodeVO5, NodeVO6, NodeVO7);
    // 默认指定父节点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"
}]