list转tree，用于展示层级结构

素颜马尾好姑娘i 2023-05-21 12:51 10阅读 0赞

### list转tree，用于展示层级结构 ###

> 部门类定义
> 
>     import java.util.List;
>     
>     /** * 部门类（省略get set方法） **/
>     public class DepartmentVO { 
>        /** * 当前部门id */
>        private String deptId;
>     
>        /** * 父部门id */
>        private String parentId;
>     
>        /** * 当前部门子部门 */
>        private List<DepartmentVO> childrens;
> 
> 方法的实现
> 
>     import java.util.ArrayList;
>     import java.util.List;
>     import java.util.Objects;
>     import java.util.stream.Collectors;
>     
>     /** * 模拟七个部门，分三个层级 */
>     public class Test4 { 
>        public static void main(String[] args) { 
>            //一级部门
>            DepartmentVO level100 = new DepartmentVO();
>            level100.setDeptId("10000");
>            level100.setParentId("0");
>     
>            //二级部门
>            DepartmentVO level200 = new DepartmentVO();
>            level200.setDeptId("20000");
>            level200.setParentId("10000");
>            DepartmentVO level201 = new DepartmentVO();
>            level201.setDeptId("20001");
>            level201.setParentId("10000");
>            DepartmentVO level202 = new DepartmentVO();
>            level202.setDeptId("20002");
>            level202.setParentId("10000");
>     
>            //三级部门
>            DepartmentVO level300 = new DepartmentVO();
>            level300.setDeptId("30000");
>            level300.setParentId("20000");
>            DepartmentVO level301 = new DepartmentVO();
>            level301.setDeptId("30000");
>            level301.setParentId("20000");
>            DepartmentVO level302 = new DepartmentVO();
>            level302.setDeptId("30000");
>            level302.setParentId("20000");
>     
>            List<DepartmentVO> list = new ArrayList<>();
>            list.add(level100);
>            list.add(level200);
>            list.add(level201);
>            list.add(level202);
>            list.add(level300);
>            list.add(level301);
>            list.add(level302);
>            List<DepartmentVO> tree = getDepartmentTree(list);
>        }
>     
>        /** * list转tree方法 */
>        public static List<DepartmentVO> getDepartmentTree(List<DepartmentVO> list) { 
>            for (DepartmentVO l : list) { 
>          			//每次循环找到每个节点的子节点们（f代表符合条件的集合），并挂载到当前节点下
>                List<DepartmentVO> children = list.stream().filter(f -> l.getDeptId().equals(f.getParentId())).collect(Collectors.toList());
>                l.setChildrens(children);
>            }
>          	//for循环结束，整棵树挂载完毕，需要找到树的根节点（此例定义parentId为0就是根节点）
>            List<DepartmentVO> rootNodes = list.stream()
>                    .filter(f -> f.getParentId() == "0" || Objects.isNull(f.getParentId())).collect(Collectors.toList());
>            return rootNodes;
>        }
>     }
> 
> 最终生产的树转JSON结构如下
> 
>     [
>        { 
>            "deptId": "10000",
>            "parentId": "0",
>            "childrens": [
>                { 
>                    "deptId": "20000",
>                    "parentId": "10000",
>                    "childrens": [
>                        { 
>                            "deptId": "30000",
>                            "parentId": "20000",
>                            "childrens": []
>                        },
>                        { 
>                            "deptId": "30000",
>                            "parentId": "20000",
>                            "childrens": []
>                        },
>                        { 
>                            "deptId": "30000",
>                            "parentId": "20000",
>                            "childrens": []
>                        }
>                    ]
>                },
>                { 
>                    "deptId": "20001",
>                    "parentId": "10000",
>                    "childrens": []
>                },
>                { 
>                    "deptId": "20002",
>                    "parentId": "10000",
>                    "childrens": []
>                }
>            ]
>        }
>     ]