Java 处理Mysql获取树形的数据
Mysql数据：
代码如下：
Entity：
@Data
@Accessors(chain = true)
public class Region {private BigInteger id;//名称private String name;//父idprivate BigInteger parentId;private List<Region> children;private Integer createTime;private Integer updateTime;private Integer isDeleted;
}Service核心代码：
List<Region> reginaList = regionMapper.findReginaList();//将数据以父类ID分组成map：{1:[xxx,xxx],2:[xxx,xxxx]}Map<BigInteger, List<Region>> parentIdMap = reginaList.stream().collect(Collectors.groupingBy(Region::getParentId, Collectors.toList()));//循环每个数据，从父类MAP中通过他的ID获取他的子类塞到children中reginaList.forEach(region -> addChildren(region, parentIdMap));//只筛选出最顶级数据List<Region> regions =reginaList.stream().filter(regina -> regina.getParentId().compareTo(BigInteger.ZERO) == 0).collect(Collectors.toList());private void addChildren(Region region, Map<BigInteger, List<Region>> parentIdMap) {List<Region> regions = parentIdMap.get(region.getId());if (regions != null) {region.setChildren(regions);regions.forEach(child -> addChildren(child, parentIdMap)); // 递归添加子级的子级}}第二种写法：
reginaList.stream().filter(city-> city.getParentId().compareTo(BigInteger.ZERO) == 0).peek(city -> city.setCityNames(getChildren(city,reginaList))).collect(Collectors.toList());public List<Region> getChildren(Region region, List<Region> regionList) {List<Region> childrens = regionList.stream().filter(re -> re.getParentId().compareTo(region.getId()) == 0).map(childRegion -> {childRegion.setAddressNames(getChildren(childRegion, regionList));return childRegion;}).collect(Collectors.toList());return childrens;}
