java 非递归list转换为树tree型结构

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                    <h3><a id="_0"></a>需求</h3>

最近在做一个导出数据生成树节点的工作 ,从数据库中导出全国省市区街道数据，查询出来是 list集合需要转换成树 tree

表

大概有这几个字段

CREATE TABLE dic (
  id int(11) NOT NULL AUTO_INCREMENT,
  name varchar(63) NOT NULL,
  parent_id int(11) NOT NULL,
) ;

代码

DicTree类

import java.util.ArrayList;
import java.util.List;
/**


@author czw


@description: 城市字典-树
*/
public class DicTree {
/**

节点id
*/
private int id;

/**

城市名称
*/
private String name;

/**

父级id
*/
private int parentId;

/**

子节点
*/
private List<DicTree> child = new ArrayList();

/**

当前属于第几级节点
*/
private int node;

public DicTree(){
}
public DicTree(int id, String name, int parentId) {
this.id = id;
this.name = name;
this.parentId = parentId;
}
/省略get/set/
}

运行代码

   @Test
   public void test3() {
       List<DicTree> dicList = dicDao.getDicData();
       List<DicTree> rootTrees = new ArrayList<DicTree>();
   for (DicTree dicTree : dicList) {
       if (dicTree.getParentId() == 0) {
           rootTrees.add(dicTree);
       }

       for (DicTree childrenDicTree : dicList) {
        /**
         * 这里只要三级节点，如果不限制子节点个数，去掉 dicTree.getNode()判断
         */
       	if (dicTree.getId() == childrenDicTree.getParentId() &amp;&amp; dicTree.getNode() &lt; 2) {
               if (dicTree.getChild() == null || dicTree.getChild().size() == 0) {
                   List&lt;DicTree&gt; myChildrens = new ArrayList&lt;DicTree&gt;();
                   myChildrens.add(childrenDicTree);
                   dicTree.setChild(myChildrens);
               } else {
                   dicTree.getChild().add(childrenDicTree);
               }

           }
       }

   }
   System.out.println("开始写出文件.......");
   try {
       File file = new File("/mnt/dic/dic10028.json");
       PrintStream ps = new PrintStream(new FileOutputStream(file));
       /**
        * 防止 fastjson把对象转化成json出现 $ref，加上 SerializerFeature.DisableCircularReferenceDetect
        */
       ps.println(JSON.toJSONString(rootTrees, SerializerFeature.DisableCircularReferenceDetect));
   } catch (FileNotFoundException e) {
       e.printStackTrace();
   }
   System.out.println("写出完毕.......");

}

优化版


    public static void main(String[] args) {
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">DicTree</span><span class="token punctuation">&gt;</span></span> dicList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    dicList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">DicTree</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token string">"测试1"</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    dicList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">DicTree</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token string">"测试2"</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    dicList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">DicTree</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token string">"测试3"</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    dicList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">DicTree</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token string">"测试4"</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">DicTree</span><span class="token punctuation">&gt;</span></span> dicTrees <span class="token operator">=</span> <span class="token function">test3</span><span class="token punctuation">(</span>dicList<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>dicTrees<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">DicTree</span><span class="token punctuation">&gt;</span></span> <span class="token function">test3</span><span class="token punctuation">(</span><span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">DicTree</span><span class="token punctuation">&gt;</span></span> dicList<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>

//        List<DicTree> dicList = dicDao.getDicData();
if (dicList.size() == 1) {
return dicList;
}
// 记录需要从 deptList 集合中移除的子节点对象
List<Integer> removeList = new ArrayList<>();
for (DicTree dicTree : dicList) {
for (DicTree childrenDicTree : dicList) {
/**
* 这里只要三级节点，如果不限制子节点个数，去掉 dicTree.getNode()判断
*/
if (dicTree.getId() == childrenDicTree.getParentId() && dicTree.getNode() < 2) {
if (dicTree.getChild() == null || dicTree.getChild().size() == 0) {
List<DicTree> myChildrens = new ArrayList<>();
removeList.add(childrenDicTree.getId());
myChildrens.add(childrenDicTree);
dicTree.setChild(myChildrens);
} else {
removeList.add(childrenDicTree.getId());
dicTree.getChild().add(childrenDicTree);
}
}
}
}
//如果是子节点，则已经移入到父级下面，因此需要从集合中移除
for (int i = 0; i < dicList.size(); i++) {
DicTree item = dicList.get(i);
if (removeList.contains(item.getId())) {
dicList.remove(item);
i--;
}
}
return dicList;
}

这种遍历就不需要考虑parentId是否为0

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java 非递归list转换为树tree型结构

表

代码

DicTree类

运行代码

优化版

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