使用java递归实现列表层级显示

╰半夏微凉° 2024-05-02 20:22 106阅读 0赞

#### 使用java递归实现列表层级显示 ####

*   *  结构类似如下(无限级):
     *  model层
     *  自定义DTO类
     *  service层
     *  结果展示

分享,欢迎批评指正,谢谢~

### 结构类似如下(无限级): ###

*  工程1
    
     *  子工程1.1
        
         *  孙工程1.1.1
         *  孙工程1.1.2
     *  子工程1.2
     *  子工程1.3
 *  工程2
    
     *  子工程2.1
        
         *  孙工程2.1.1
         *  孙工程2.1.2  
            …

### model层 ###

//数据库表中字段相同
    public class Eng{
        
        private Long engId;
        private String engName;
        private Long engPid;
        //get set自行添加,此处省略
    }

### 自定义DTO类 ###

在model字段基础上加入childrenList

public class EngChildrenDTO{
        
        private Long engId;
        private String engName;
        private Long engPid;
        private List<EngChildrenDTO> childrenList;
       //get set自行添加,此处省略
    }

### service层 ###

public List<EngChildrenDTO> engList() {
        
            //查询出所有的工程(line 1~line5)
            //因为本案例使用了MyBatis Generator自动生成model类、dao层的mapper类、*DynamicSqlSupport动态语句支持类
            //所以该案例"查询所有工程"时使用MyBatis3 DynamicSql写法,可相应地替换成您项目中使用的其他方式来实现"查询出所有的工程"
            SelectStatementProvider render = select(EngDynamicSqlSupport.eng.allColumns())
                    .from(EngDynamicSqlSupport.eng)
                    .where(EngDynamicSqlSupport.deleteFlag, isEqualTo(0))
                    .build().render(RenderingStrategies.MYBATIS3);
            List<Eng> allEngs = engMapper.selectMany(render);
            
            //遍历查询出来的所有工程allEngs ,赋值给engChildrenDTO,并add到root
            ArrayList<EngChildrenDTO> root = new ArrayList<>();//用于存放所有工程
            for (Eng allEng : allEngs) {
        
                EngChildrenDTO engChildrenDTO = new EngChildrenDTO();
                BeanUtils.copyProperties(allEng, engChildrenDTO);//给riskEngChildrenDTO赋值
                root.add(engChildrenDTO);
            }
            
            //遍历root 找到所有的一级工程,add到finalList
            List<EngChildrenDTO> finalList = new ArrayList<>();//用于存放一级工程
            for (EngChildrenDTO eng : root) {
        
                if (StringUtils.isEmpty(eng.getEngPid())) {
        //一级工程(pid为空)
                    finalList.add(eng);
                }
            }
            
            // 遍历一级工程,为一级工程设置子工程( 调用下方定义的递归体getChild() )
            for (EngChildrenDTO eng : finalList) {
        
                eng.setChildrenList(getChild(eng.getEngId(), root));
            }
            
            return finalList;
        }

//递归体,主方法中进行循环调用
        private List<EngChildrenDTO> getChild(Long id, List<EngChildrenDTO> root) {
        
            //遍历传入的root,pid不为空(即不是一级工程) 且此工程pid等于传过来的工程的id时,加入childList 
            List<EngChildrenDTO> childList = new ArrayList<>(); //用于存放子工程
            for (EngChildrenDTO engChildrenDTO : root) {
        
                if (!StringUtils.isEmpty(engChildrenDTO.getEngPid())) {
        
                    if (engChildrenDTO.getEngPid().equals(id)) {
        
                        childList.add(engChildrenDTO);
                    }
                }
            }
            
            //递归终止的条件(没有子工程时)
            if (childList.size() == 0) {
        
                return null;
            }
            
            //如果有子工程还有子工程,遍历childList,继续进行递归调用
            for (EngChildrenDTO engChildrenDTO : childList) {
        
               engChildrenDTO.setChildrenList(getChild(engChildrenDTO.getEngId(), root));
            }
            
            return childList;
        }

### 结果展示 ###

{
      "status": true,
      "data": [
        {
          "engId": "1388436330181062657",
          "engName": "工程1",
          "engPid": null,
          "childrenList": [
            {
              "engId": "1390277587912224770",
              "engName": "子工程1.1",
              "engPid": "1388436330181062657",
              "childrenList": [
                {
                  "engId": "1391568088810614785",
                  "engName": "孙工程1.1",
                  "engPid": "1390277587912224770",
                  "childrenList": null
                }
              ]
            },
            {
              "engId": "1390276723344535553",
              "engName": "子工程1.2",
              "engPid": "1388436330181062657",
              "childrenList": null
            }
          ]
        },
        {
          "engId": "1390994842794659842",
          "engName": "工程2",
          "engPid": null,
          "childrenList": [
            {
              "engId": "1391571581688590337",
              "engName": "子工程2.1",
              "engPid": "1390994842794659842",
              "childrenList": null
            },
            {
              "engId": "1391568182108712961",
              "engName": "子工程2.2",
              "engPid": "1390994842794659842",
              "childrenList": [
                {
                  "engId": "1391572327666483201",
                  "engName": "孙工程2.2.1",
                  "engPid": "1391568182108712961",
                  "childrenList": [
                    {
                      "engId": "1392450583207936001",
                      "engName": "孙工程2.2.2",
                      "engPid": "1391572327666483201",
                      "childrenList": null
                    }
                  ]
                }
              ]
            }
          ]
        }
      ],
      "code": 8000000,
      "message": "成功",
      "txId": "null"
    }