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java中使用递归快速构建树形数据结构

1，数据表设计

在设计表时每个记录中应添加parentId字段，用于标识父子关系。

2，实体类

public class Entity {private Long id;private Long parentId;private List<Entity> children = Lists.newArrayList();// 省略其他属性及get、set方法}

3，service

// 常量 标识第一层级的父idprivate final static Long ROOT_PARENT_ID = 0L;/*** 获取树形结构* @param condition 筛选条件* @return*/public List<Entity> loadTreeData(Condition condition) {List<Entity> entityList = this.dealTreeData(ROOT_PARENT_ID,condition);return entityList;}private List<Entity> dealTreeData(Long parentId,condition condition){// 获取所有的数据表记录List<Entity> allItems = EntityMapper.getAllItems();if(CollectionUtils.isEmpty(allItems)) {return Lists.newArrayList();}// 递归方法List<Entity> tree = this.getTree(allItems, parentId);// 条件筛选this.treeMatch(tree,condition);return tree;}private List<Entity> getTree(List<Entity> allItems,Long parentId){List<Entity> tree = new ArrayList<>();for(Entity entity:allItems){if(entity.getParentId() == parentId){entity.setChildren(getTree(allItems,entity.getId()));tree.add(entity);}}return tree;}public void treeMatch(List<Entity> allTree, condition condition){Iterator<Entity> iter = allTree.iterator();while (iter.hasNext()){// 获取当前遍历到的目录Entity entity = iter.next();boolean shouldRemove = true;// 如果当前目录名称包含关键字，则什么也不做（不移除），否则就看下一级if(StringUtils.hasText(condition.getCondition1()) && !entity.getCondition1().equals(condition.getCondition1())){// 取出下一级目录集合List<Entity> childrenList = entity.getChildren();// 递归if(!CollectionUtils.isEmpty(childrenList)){treeMatch(childrenList,condition);}} else if(StringUtils.hasText(condition.getCondition2()) && !entity.getCondition2().equals(condition.getCondition2())){// 取出下一级目录集合List<Entity> childrenList = entity.getChildren();// 递归if(!CollectionUtils.isEmpty(childrenList)){treeMatch(childrenList,condition);}} else {shouldRemove = false;}// 下一级目录看完了，如果下一级目录全部被移除，则移除当前目录if(CollectionUtils.isEmpty(entity.getItems()) && shouldRemove){iter.remove();}}}