java 查询树结构数据，无限层级树结构通用方法

1、数据库表数据

2、controller层TestTree简单测试

@RestController
@RequestMapping("/test")
public class testTreeController {@Autowiredprivate TestTreeService testTreeService;@GetMapping("/list")public List<TestTree> List(TestTree tree){List<TestTree> testTrees = testTreeService.getTreeList(tree);return testTrees;}
}

3、TestTree实体类

@TableName(value ="test_tree")
@Data
public class TestTree implements TreeNode {/*** id*/@TableIdprivate String id;/*** 父级id*/private String pid;/*** 名称*/private String name;/*** 类型*/private String type;@TableField(exist = false)private static final long serialVersionUID = 1L;@TableField(exist = false)private List childNodeList = new ArrayList<>();@Overridepublic void setChildNodeList(List childNodeList) {this.childNodeList = childNodeList;}@Overridepublic List getChildNodeList() {return childNodeList;}
}

4、TestTreeService 接口

public interface TestTreeService extends IService<TestTree> {/*** 查找树结构List* @param tree 查询条件* @return 树结构结果*/List<TestTree> getTreeList(TestTree tree);
}

5、TestTreeServiceImpl 实现类

@Service
public class TestTreeServiceImpl extends ServiceImpl<TestTreeMapper, TestTree>implements TestTreeService{public List<TestTree> selectList(TestTree tree) {LambdaQueryWrapper<TestTree> queryWrapper = new LambdaQueryWrapper();queryWrapper.eq(ObjectUtil.isNotEmpty(tree.getId()), TestTree::getId, tree.getId());queryWrapper.like(ObjectUtil.isNotEmpty(tree.getName()), TestTree::getName, tree.getName());queryWrapper.like(ObjectUtil.isNotEmpty(tree.getType()), TestTree::getType, tree.getType());return super.list(queryWrapper);}@Overridepublic List<TestTree> getTreeList(TestTree tree) {//查询数据List<TestTree> list  = this.selectList(tree);//封装树结构，通用方法，参数为传入的ListList<TestTree> treeList = TreeList.getTreeList(list);//返回树结构Listreturn  treeList;}
}

6、构建树结构

6.1、定义TreeNode

public interface TreeNode<E extends TreeNode> {/*** 获取节点ID*/String getId();/*** 获取父ID*/String getPid();void setChildNodeList(List<E> childNodeList);/*** 子节点数据*/List<E> getChildNodeList();
}

6.2、构建树结构

import cn.hutool.core.collection.CollectionUtil;
import cn.hutool.core.util.StrUtil;import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Collectors;/*** 处理树形结构的数据*/
public final class TreeList {public static <E extends TreeNode> List<E> getTreeList(List<E> allData){//通过流操作，过滤出所有pid为空或者为null的节点，就是树的顶层节点List<E> topNode = allData.stream().filter(item -> Objects.isNull(item) || StrUtil.isBlank(item.getPid())).collect(Collectors.toList());//移除所有pid为空或为null的节点allData.removeIf(item->Objects.isNull(item) || StrUtil.isBlank(item.getPid()));//将剩余节点按pid分租，结果存储在map中，pid作为键，节点列表作为值Map<String, List<E>> map = allData.stream().collect(Collectors.groupingBy(TreeNode::getPid));//构建树形结构buildTree(topNode,map);//返回顶层节点列表return topNode;}//构建树形结构public static <E extends TreeNode> void buildTree(List<E> topNode, Map<String,List<E>> map){for (E node : topNode) {//遍历顶层节点，如果节点为null，则跳过if (Objects.isNull(node)){continue;}//获取当前节点的idString id = node.getId();//从map中获取其子节点列表List<E> treeNodes = map.get(id);//将其设置为当前节点的子节点列表node.setChildNodeList(treeNodes);//如果当前节点没有子节点，则继续下一个节点if (CollectionUtil.isEmpty(treeNodes)){continue;}//对当前节点的子节点列表递归调用buildTree方法，继续构建树形结构buildTree(treeNodes,map);}}
}

7、postman测试

结果

[{"id": "1","pid": null,"name": "第一层级","type": "1","childNodeList": [{"id": "2","pid": "1","name": "第二层级","type": "2","childNodeList": [{"id": "3","pid": "2","name": "第三层级","type": "3","childNodeList": [{"id": "4","pid": "3","name": "第四层级","type": "4","childNodeList": [{"id": "5","pid": "4","name": "第五层级","type": "5","childNodeList": null}]}]},{"id": "6","pid": "2","name": "次二层级","type": "6","childNodeList": null}]}]}
]