通过Java构建树形结构

通过Java构建树形结构所需要的数据

实体类Test

	/** 主键 */
    private String id;

    /** 父类ID */
    private String parentId;
    
    // 子节点
	private List<Test> children;

    /** 名称 */
    private String name;

buildTreeByStream入参为list
我这里当节点的parentId = ‘-1’ 那么这个节点就是根节点

	// list 是从数据库请求回来的数据
	@Override
    public List<Test> selectTestList(Test test)
    {
    	List<Test> list = TestMapper.selectList(test);
    	// 返回树结构
        return buildTreeByStream(list);
    }
// 构建前端所需要树
    public static List<Test> buildTreeByStream(List<Test> list){
        // 获取根节点
        List<Test> root = list.stream().filter(item -> "-1".equals(item.getParentId())).collect(Collectors.toList());
        // 根据pid 进行分组
        Map<String,List<Test>> map = list.stream().collect(Collectors.groupingBy(Test::getParentId));
        recursionFnTree(list,map);
        return root;
    }
    // 递归
    public static void recursionFnTree(List<Test> list, Map<String,List<Test>> map){
        for (Test test: list) {
            List<Test> childList = map.get(Test.getId());
            test.setChildren(childList);
            if (null != childList && 0<childList.size()){
                recursionFnTree(childList,map);
            }
        }
    }

使用sql查询树形结构 (以若依的部门表为例，主要用于查该部门与子部门)

WITH RECURSIVE cte AS (
SELECT dept_id,parent_id,dept_name FROM `sys_dept` WHERE dept_id = '100' # 参数
UNION ALL 
SELECT aa.dept_id,aa.parent_id,aa.dept_name FROM sys_dept aa,cte WHERE aa.parent_id = cte.dept_id
)
SELECT * FROM cte;