目录
前言：
在日常的开发或者工作需求中，我们会用到树形结构数据。树形结构是一个比较常用的数据类型，一般多用于查询包含父子类关系的数据。我们常常通过父级id和层级作为标识，是数据更加形象，从而进行树形数据的展示。
开发前准备：
数据库：
-- ------------------------------ Table structure for dev_type-- ----------------------------DROP TABLE IF EXISTS `dev_type`;CREATE TABLE `dev_type` ( `id` int(50) NOT NULL, `name` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '名称', `level` tinyint(3) NULL DEFAULT NULL COMMENT '层级 1 2 3', `parent_id` int(50) NULL DEFAULT NULL COMMENT '父级id', PRIMARY KEY (`id`) USING BTREE) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;-- ------------------------------ Records of dev_type-- ----------------------------INSERT INTO `dev_type` VALUES (110, '长安区', 3, 119);INSERT INTO `dev_type` VALUES (119, '石家庄市', 2, 10086);INSERT INTO `dev_type` VALUES (10010, '中原区', 3, 456789);INSERT INTO `dev_type` VALUES (10086, '河北省', 1, NULL);INSERT INTO `dev_type` VALUES (12313, '高新区', 3, 456789);INSERT INTO `dev_type` VALUES (123456, '河南省', 1, NULL);INSERT INTO `dev_type` VALUES (456789, '郑州市', 2, 123456);SET FOREIGN_KEY_CHECKS = 1;实体类：
@Data@TableName("dev_type")@JsonInclude(JsonInclude.Include.NON_EMPTY)public class DevType { private static final long serialVersionUID = 1L;@JsonSerialize(using = ToStringSerializer.class) private Long id; @ApiModelProperty("名称") private String name; @ApiModelProperty("等级(1 ，2，3)") private String level; @ApiModelProperty("父级id") private Long parentId;}VO对象：
@Data@JsonInclude(JsonInclude.Include.NON_EMPTY)public class TreeNode extends DevType { private static final long serialVersionUID = 1L; @ApiModelProperty("子节点") private List child;} 代码实现：
Controller层：
@GetMapping("/newTree/list")@ApiOperation(value = "树形结构列表", notes = "传入devType")public List newTreeList(DevType devType) {List pages = devTypeService.newTreeList(devType);return pages;} Service层：
@Overridepublic List newTreeList(DevType devType) {if (devType == null || (devType.getLevel() == null && devType.getId() == null && devType.getParentId() == null)) {devType.setLevel("1");}QueryWrapper queryWrapper = new QueryWrapper<>();// 构造查询条件queryWrapper.eq(devType.getId() != null, "id", devType.getId()).eq(StringUtils.isNotBlank(devType.getLevel()), "level", devType.getLevel()).eq(devType.getParentId() != null, "parent_id", devType.getParentId());return getTree(queryWrapper);}private List getTree(QueryWrapper queryWrapper) {List list = this.list(queryWrapper);List voList = new ArrayList<>(list.size());for (DevType child : list) {TreeNode childVO = new TreeNode();BeanUtils.copyProperties(child, childVO);QueryWrapper childQueryWrapper = new QueryWrapper<>();childQueryWrapper.eq("parent_id", child.getId());childVO.setChild(getTree(childQueryWrapper));voList.add(childVO);}return voList;} 运行结果：
[ { "id": "10086", "name": "河北省", "level": "1", "child": [ { "id": "119", "name": "石家庄市", "level": "2", "parentId": 10086, "child": [ { "id": "110", "name": "长安区", "level": "3", "parentId": 119 } ] } ] }, { "id": "123456", "name": "河南省", "level": "1", "child": [ { "id": "456789", "name": "郑州市", "level": "2", "parentId": 123456, "child": [ { "id": "10010", "name": "中原区", "level": "3", "parentId": 456789 }, { "id": "12313", "name": "高新区", "level": "3", "parentId": 456789 } ] } ] }]第二种：
@GetMapping("/tree/list")@ApiOperationSupport(order = 2)@ApiOperation(value = "树形结构列表", notes = "")public R> getDataList() {List pages = devTypeService.list();List devTypes = buildTree(pages, null);return R.data(devTypes);} private List buildTree(List devTypes, Long parentId) {List tree = new ArrayList<>();for (DevType devType : devTypes) {if (devType.getParentId() == parentId) {TreeNodetreeNode = new TreeNode();BeanUtils.copyProperties(devType,treeNode);// 递归构建子树List children = buildTree(devTypes, devType.getId());treeNode.setChildren(children);tree.add(treeNode);}}return tree;} 第三种：
通过stream获取：
@GetMapping("/new/tree")@ApiOperationSupport(order = 2)@ApiOperation(value = "树形结构列表", notes = "传入devType")public R> newTree() {List pages = devTypeService.list();//1List list = pages.stream().map(devType -> {TreeNode vo = new TreeNode();BeanUtils.copyProperties(devType, vo);return vo;}).collect(Collectors.toList());//2//1、2 两部可以通过mapper方法实现，直接转换成VO数据List TreeMenu = list.stream().filter(m -> m.getParentId() == null).map((m) -> {m.setChildren(getChildrens(m, list));return m;}).collect(Collectors.toList());return R.data(TreeMenu);}private List getChildrens(TreeNode root, List all) {List children = all.stream().filter(m -> {return Objects.equals(m.getParentId(), root.getId());}).map((m) -> {m.setChildren(getChildrens(m, all));return m;}).collect(Collectors.toList());return children;} 在这里，我们需要先搞清楚对应的父子关系，只有捋顺了关系之后才能进行代码的书写。第一种方式是我们什么都不传的情况下，默认查出的是全部的数据。如果想要查某一条下面具体的子类，可以传入对应的id和层级level。第二种是查出全部的树形结构数据。在此特作分享，给大家提供不一样的思路。
来源地址：https://blog.csdn.net/m0_71239320/article/details/131055258
