Java实现List集合转树形结构的示例详解

@Data
@AllArgsConstructor
@NoArgsConstructor
public class TreeNode {
    /**
     * 节点内码
     */
    private Long id;
    /**
     * 节点名称
     */
    private String label;
    /**
     * 父节点内码
     */
    private Long pid;
    /**
     * 子节点集合
     */
    private List<TreeNode> children;
}

public class List2TreeList {
 
    //方式一:  使用foreach转换
    public static List<TreeNode> buildTreeUseList(List<TreeNode> treeList,long id){
        //收集传递的集合中父id相同的TreeNode
        List<TreeNode> children = new ArrayList<>();
        for (TreeNode treeNode : treeList) {
            //判断该节点的父id，是否与传入的父id相同，相同则递归设置其孩子节点，并将该节点放入children集合中
            if(treeNode.getPid() == id){
                //递归设置其孩子节点
                treeNode.setChildren(buildTreeUseList(treeList, treeNode.getId()));
                //放入children集合
                children.add(treeNode);
            }
        }
        return children;
    }
 
    //方式二:  使用stream流转换
    public static List<TreeNode> buildTreeUseStream(List<TreeNode> treeList,long id){
        List<TreeNode> list = treeList.stream()
                //过滤父节点与传递的id相同的TreeNode对象
                .filter( treeNode -> treeNode.getPid().longValue() == id )
                .map( treeNode -> {
                    //递归设置孩子节点
                    treeNode.setChildren(buildTreeUseStream(treeList,treeNode.getId()));
                    return treeNode;
                })
                .collect(Collectors.toList());
        return list;
    }
}

@RestController
public class TestController {
 
    @GetMapping("/treeList")
    public List<TreeNode> convert2Tree(){
        List<TreeNode> list = new ArrayList<>();
        list.add(new TreeNode(370000l,"山东省",0l,null));
        list.add(new TreeNode(370100l,"济南市",370000l,null));
        list.add(new TreeNode(370200l,"青岛市",370000l,null));
        list.add(new TreeNode(370300l,"淄博市",370000l,null));
        list.add(new TreeNode(371300l,"临沂市",370000l,null));
        list.add(new TreeNode(370102l,"历下区",370100l,null));
        list.add(new TreeNode(370103l,"市中区",370100l,null));
        list.add(new TreeNode(370202l,"市南区",370200l,null));
        //使用list转换
        List<TreeNode> treeList = List2TreeList.buildTreeUseList(list, 0l);
        System.out.println(treeList);
        return treeList;
    }
}

[
    {
        "id": 370000,
        "label": "山东省",
        "pid": 0,
        "children": [
            {
                "id": 370100,
                "label": "济南市",
                "pid": 370000,
                "children": [
                    {
                        "id": 370102,
                        "label": "历下区",
                        "pid": 370100,
                        "children": []
                    },
                    {
                        "id": 370103,
                        "label": "市中区",
                        "pid": 370100,
                        "children": []
                    }
                ]
            },
            {
                "id": 370200,
                "label": "青岛市",
                "pid": 370000,
                "children": [
                    {
                        "id": 370202,
                        "label": "市南区",
                        "pid": 370200,
                        "children": []
                    }
                ]
            },
            {
                "id": 370300,
                "label": "淄博市",
                "pid": 370000,
                "children": []
            },
            {
                "id": 371300,
                "label": "临沂市",
                "pid": 370000,
                "children": []
            }
        ]
    }
]