java树型数据的工具类

public List<DeptVO> tree(String tenantId) {
   return ForestNodeMerger.merge(baseMapper.tree(tenantId));
}baseMapper.tree(tenantId)为目标数据源

ForestNodeMerger 工具类

import java.util.List;

public class ForestNodeMerger {
    public ForestNodeMerger() {
    }

    public static <T extends INode<T>> List<T> merge(List<T> items) {
        ForestNodeManager<T> forestNodeManager = new ForestNodeManager(items);
        items.forEach((forestNode) -> {
            if (forestNode.getParentId() != 0L) {
                INode<T> node = forestNodeManager.getTreeNodeAt(forestNode.getParentId());
                if (node != null) {
                    node.getChildren().add(forestNode);
                } else {
                    forestNodeManager.addParentId(forestNode.getId());
                }
            }

        });
        return forestNodeManager.getRoot();
    }
}

ForestNodeManager 工具类

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class ForestNodeManager<T extends INode<T>> {
    private final ImmutableMap<Long, T> nodeMap;
    private final Map<Long, Object> parentIdMap = Maps.newHashMap();

    public ForestNodeManager(List<T> nodes) {
        this.nodeMap = Maps.uniqueIndex(nodes, INode::getId);
    }

    public INode<T> getTreeNodeAt(Long id) {
        return this.nodeMap.containsKey(id) ? (INode)this.nodeMap.get(id) : null;
    }

    public void addParentId(Long parentId) {
        this.parentIdMap.put(parentId, "");
    }

    public List<T> getRoot() {
        List<T> roots = new ArrayList();
        this.nodeMap.forEach((key, node) -> {
            if (node.getParentId() == 0L || this.parentIdMap.containsKey(node.getId())) {
                roots.add(node);
            }

        });
        return roots;
    }
}

INode<T> 接口

import java.io.Serializable;
import java.util.List;

public interface INode<T> extends Serializable {
    Long getId();

    Long getParentId();

    List<T> getChildren();

    default Boolean getHasChildren() {
        return false;
    }
}

 DeptVO 要继承INode接口

@Data
@EqualsAndHashCode(callSuper = true)
@ApiModel(value = "DeptVO对象", description = "DeptVO对象")
public class DeptVO extends Dept implements INode<DeptVO> {
   private static final long serialVersionUID = 1L;

   /**
    * 主键ID
    */
   @JsonSerialize(using = ToStringSerializer.class)
   private Long id;
   
   //这三个为INode里的属性
   /**
    * 父节点ID
    */
   @JsonSerialize(using = ToStringSerializer.class)
   private Long parentId;

   /**
    * 子孙节点
    */
   @JsonInclude(JsonInclude.Include.NON_EMPTY)
   private List<DeptVO> children;

   /**
    * 是否有子孙节点
    */
   @JsonInclude(JsonInclude.Include.NON_EMPTY)
   private Boolean hasChildren;

   @Override
   public List<DeptVO> getChildren() {
      if (this.children == null) {
         this.children = new ArrayList<>();
      }
      return this.children;
   }

   /**
    * 上级机构
    */
   private String parentName;

   /**
    * 机构类型名称
    */
   private String deptCategoryName;