拼接树形JSON列表如何利用Java与MySQL递归的方法实现

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前言

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我们在做Java web项目时，前端控件例如国家-省-市-区-县等树形列表，常常需要多级树形json数据

例如：

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[
 {
 "name": "商品目录",
 "pid": "-1",
 "id": "1",
 "children": [
  {
  "name": "日用品",
  "pid": "1",
  "id": "11",
  "children": [
   {
   "name": "洗发水",
   "pid": "11",
   "id": "111",
   "children": [
    {
     "name": "霸王",
     "pid": "111",
     "id": "1111",
     "children": []
    }
   ]
   }
  ]
  },
  {
  "name": "食品",
  "pid": "1",
  "id": "12",
  "children": []
  }
 ]
 }
]

整体思路分为两步，第一步获取目录及其所有子目录，获取后的列表形式如下：

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[
 {"id":"1","pid":"-1","name":"商品目录"},
 {"id":"11","pid":"1","name":"日用品"},
 {"id":"12","pid":"1","name":"食品"},
 {"id":"111","pid":"11","name":"洗发水"},
 {"id":"1111","pid":"111","name":"霸王"}
]

第二步，利用递归思想拼装该数据，拼装方法的工具类如下：

package *.*.*;

import net.sf.json.JSONArray;

import java.util.ArrayList;
import java.util.List;

/**
 * 构造目录JSON树
 * Created by fukang on 2017/5/26 0026.
 */
public class TreeBuilder {

 List nodes = new ArrayList<>();

 public String buildTree(List nodes) {

  TreeBuilder treeBuilder = new TreeBuilder(nodes);

  return treeBuilder.buildJSONTree();
 }

 public TreeBuilder() {
 }

 public TreeBuilder(List nodes) {
  super();
  this.nodes = nodes;
 }

 // 构建JSON树形结构
 public String buildJSONTree() {
  List nodeTree = buildTree();
  JSONArray jsonArray = JSONArray.fromObject(nodeTree);
  return jsonArray.toString();
 }

 // 构建树形结构
 public List buildTree() {
  List treeNodes = new ArrayList<>();
  List rootNodes = getRootNodes();
  for (Node rootNode : rootNodes) {
   buildChildNodes(rootNode);
   treeNodes.add(rootNode);
  }
  return treeNodes;
 }

 // 递归子节点
 public void buildChildNodes(Node node) {
  List children = getChildNodes(node);
  if (!children.isEmpty()) {
   for (Node child : children) {
    buildChildNodes(child);
   }
   node.setChildren(children);
  }
 }

 // 获取父节点下所有的子节点
 public List getChildNodes(Node pnode) {
  List childNodes = new ArrayList<>();
  for (Node n : nodes) {
   if (pnode.getId().equals(n.getPid())) {
    childNodes.add(n);
   }
  }
  return childNodes;
 }

 // 判断是否为根节点
 public boolean rootNode(Node node) {
  boolean isRootNode = true;
  for (Node n : nodes) {
   if (node.getPid().equals(n.getId())) {
    isRootNode = false;
    break;
   }
  }
  return isRootNode;
 }

 // 获取集合中所有的根节点
 public List getRootNodes() {
  List rootNodes = new ArrayList<>();
  for (Node n : nodes) {
   if (rootNode(n)) {
    rootNodes.add(n);
   }
  }
  return rootNodes;
 }

 public static class Node {

  private String id;
  private String pid;
  private String name;
  private List children;

  public Node() {
  }

  public Node(String id, String pid, String name) {
   super();
   this.id = id;
   this.pid = pid;
   this.name = name;
  }

  public String getId() {
   return id;
  }

  public void setId(String id) {
   this.id = id;
  }

  public String getPid() {
   return pid;
  }

  public void setPid(String pid) {
   this.pid = pid;
  }

  public String getName() {
   return name;
  }

  public void setName(String name) {
   this.name = name;
  }


  public List getChildren() {
   return children;
  }

  public void setChildren(List children) {
   this.children = children;
  }
 }
}

在Controller中的调用方法是：

 @RequestMapping("/bulidJsonTree")
 @ResponseBody
 public String buildJsonTree(HttpServletRequest request) {

  // 获取全部目录节点
  List nodes = iGoodsDirSvc.getAllDirList();

  // 拼装树形json字符串
  String json = new TreeBuilder().buildTree(nodes);

  return json;
 }

其中iGoodsDirSvc.getAllDirList()方法需要将取到的数据转为Node类型：

String hql = "select id as id,pId as pid,name as name from Directory";

Query query = factory.getCurrentSession().createQuery(hql)
.setResultTransformer(Transformers.aliasToBean(TreeBuilder.Node.class));

return query.list();

总结