前言：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();