递归 Stream流式 自关联递归

1.测试实体类

/**
 * @author : zhang sq
 * @date : 2022/7/30 9:54
 **/
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Recursion implements Serializable {
 
    private int id;
 
    /**
     * 父id
     */
    private int parentId;
 
    /**
     *  名称
     */ 
    private String  name;
 
    /**
     *  排序值
     */
    private int sort;
 
    /**
     *  创建时间
     */
    private Date createTime;
 
    private List childern;
 
    public Recursion(int id, int parentId, String name) {
        this.id = id;
        this.parentId = parentId;
        this.name = name;
    }
 
    public Recursion(int id, int parentId, String name, int sort, Date createTime) {
        this.id = id;
        this.parentId = parentId;
        this.name = name;
        this.sort = sort;
        this.createTime = createTime;
    }
}

2.测试代码

/**
 * @author : zhang sq
 * @date : 2022/7/30 9:55
 **/
public class Test {
    public static void main(String[] args) {
        //模拟测试数据
        List recursionlist = new ArrayList<>();
        Recursion re1 = new Recursion(1,0,"湖北省",1 ,new Date());
        Recursion re2 = new Recursion(2,1,"孝感市",3 ,new Date());
        Recursion re3 = new Recursion(3,2,"云梦县",2 ,new Date());
        Recursion re4 = new Recursion(4,3,"义堂镇",2 ,new Date());
        Recursion re5 = new Recursion(5,1,"武汉市",2 ,new Date());
        Recursion re6 = new Recursion(6,5,"江夏区",2 ,new Date());
        Recursion re7 = new Recursion(7,6,"佛祖岭",2 ,new Date());
        recursionlist.add(re1);recursionlist.add(re2);
        recursionlist.add(re3);recursionlist.add(re4);
        recursionlist.add(re5);recursionlist.add(re6);
        recursionlist.add(re7);
        
        //根据最外层数据递归
        re1.setChildern(Recursion(recursionlist, re1.getId()));
        System.out.println(JSON.toJSONString(re1));
 
    }
 
    /**
     * 递归 (常用于菜单 , 自关联的递归查询 )
     * @param recursionlist 所有的自关联数据
     * @param parentId 最外层的主键id
     * @return  tree 树结构
     */
    private static List  Recursion(List recursionlist, int parentId){
        List recursionlist2 = new ArrayList<>();
        Optional.ofNullable(recursionlist).orElse(new ArrayList<>())
                .stream()
                .filter(recursion -> recursion.getParentId()==parentId) //过滤 父id == 当前id的 ,(取当前下级)
                .forEach(recursion -> {     //遍历下级存 List
                    recursionlist2.add(
                            Recursion.builder()
                                    .id(recursion.getId())
                                    .name(recursion.getName())
                                    .parentId(recursion.getParentId())
                                    .sort(recursion.getSort())
                                    .createTime(new Date())
                                    .childern(Recursion(recursionlist,recursion.getId()))
                                    .build());
                });
 
        //每次递归数据 进行排序处理
        List collect = Optional.ofNullable(recursionlist2).orElse(new ArrayList<>())
                .stream()
                .sorted(Comparator.comparing(Recursion::getSort) //根据sort排序.sort必须有值,不然会空指针
                .thenComparing(Recursion::getCreateTime))
                .collect(Collectors.toList());
 
        return collect;
    }
}