利用java+mysql递归实现拼接树形JSON列表的方法示例

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：

[
 {
 "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：

[
 {"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<node> nodes = new arraylist<>();

 public string buildtree(list<node> nodes) {

  treebuilder treebuilder = new treebuilder(nodes);

  return treebuilder.buildjsontree();
 }

 public treebuilder() {
 }

 public treebuilder(list<node> nodes) {
  super();
  this.nodes = nodes;
 }

 // 构建json树形结构
 public string buildjsontree() {
  list<node> nodetree = buildtree();
  jsonarray jsonarray = jsonarray.fromobject(nodetree);
  return jsonarray.tostring();
 }

 // 构建树形结构
 public list<node> buildtree() {
  list<node> treenodes = new arraylist<>();
  list<node> rootnodes = getrootnodes();
  for (node rootnode : rootnodes) {
   buildchildnodes(rootnode);
   treenodes.add(rootnode);
  }
  return treenodes;
 }

 // 递归子节点
 public void buildchildnodes(node node) {
  list<node> 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<node> getchildnodes(node pnode) {
  list<node> 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<node> getrootnodes() {
  list<node> 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<node> 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<node> getchildren() {
   return children;
  }

  public void setchildren(list<node> 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<node> 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

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