java--树封装

Multimap：允许key值相同，不会覆盖掉之前的数据。用于封装类似于Map<Object,List<Object>>这种有嵌套结构的数据。Maven坐标如下：

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>10.0.1</version>
</dependency>

1.定义树结构

public class MyTree {
    private String id;
    private String parentId;
    private String name;
    private List<MyTree> child = Lists.newArrayList();
    //getter()、setter()方法。。。
　　 public void addChild(MyTree tree){
        child.add(tree);
    }

2.支持多层次的树封装：　　

//2万条数据封装耗时15ms
public Collection<MyTree> getCompleteTrees() {
        //获取数据
        List<MyTree> treeList = initList();
        //树节点封装
        Multimap<String, MyTree> multimap = treeNodePackageByParentId(treeList);
        //获取根节点
        Collection<MyTree> rootNodeList = multimap.get("0");
        //添加子节点
        addTreeNodeDependency(rootNodeList, multimap);
        return rootNodeList;
}

//按parentId聚合
private Multimap<String, MyTree> treeNodePackageByParentId(List<MyTree> treeList) {
        Multimap<String, MyTree> multimap = HashMultimap.create();
        for (MyTree treeNode : treeList) {
            multimap.put(treeNode.getParentId(), treeNode);
        }
return multimap;
}

//添加依赖关系
private void addTreeNodeDependency(Collection<MyTree> rootTreeList, Multimap<String, MyTree> multiMap) {
        for (MyTree parentTreeNode : rootTreeList) {
            addChildNode(parentTreeNode, multiMap);
        }
}

private void addChildNode(MyTree parentTreeNode, Multimap<String, MyTree> multiMap) {
        String id = parentTreeNode.getId();
        for (MyTree chileTreeNode : multiMap.get(id)) {
            String childId = chileTreeNode.getId();
            parentTreeNode.addChild(chileTreeNode);
            if (multiMap.containsKey(childId)) {
                addChildNode(chileTreeNode, multiMap);
            }
        }
}

//----------算法性能差，时间复杂度O(n*n),2万条数据封装耗时20s-------------
//获取数据
List<MyTree> treeList=initList();
MyTree resultTree=null;
//添加父节点和子节点依赖关系　　　　　
for(MyTree outTree:treeList){
   String id=outTree.getId();
　　//找到根节点
   if("0".equals(outTree.getParentId())){
      resultTree=outTree;
   }
   for(MyTree innerTree:treeList){
      String parentId=innerTree.getParentId();
      if(id.equals(parentId)){
         outTree.addChild(innerTree);
      }
   }
}

3.数据结构如下：

id	parentId	name
1	0	中国
2	1	江苏省
3	2	南京市
4	2	徐州市
5	4	新沂市
6	1	浙江省
7	6	杭州市

4.运行结果如下：