四）绘树

实测代码：

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

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import org.junit.Test;

public class Digui {

    @Test
    public void drawTree() {
        List<Node> nodeList = new ArrayList<Node>();
        nodeList.add(new Node("0001", "null", "中国"));
        nodeList.add(new Node("0002", "0001", "河北"));
        nodeList.add(new Node("0003", "0001", "辽宁"));
        nodeList.add(new Node("0004", "0002", "石家庄"));
        nodeList.add(new Node("0005", "0003", "沈阳"));
        nodeList.add(new Node("0006", "null", "美国"));
        nodeList.add(new Node("0007", "0006", "纽约"));
        System.out.println(children("null", nodeList));
    }

    // 递归条件：1. 延伸 2.有尽头
    public JSONArray children(String my, List<Node> nodes) {
        JSONArray myChildren = new JSONArray();
        for (Node node : nodes) {
            String id = node.getId();
            String pid = node.getPid();
            if (my.equals(pid)) {
                JSONObject myChild = new JSONObject();
                myChild.put("id", id);
                myChild.put("pid", pid);
                myChild.put("name", node.getName());
                JSONArray myChildChildren = children(id, nodes);
                if (myChildChildren.size() > 0)
                    myChild.put("children", myChildChildren);
                myChildren.add(myChild);
            }
        }
        return myChildren;
    }

}

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

    private String id;
    private String pid;
    private String 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;
    }

    @Override
    public String toString() {
        return "Node [id=" + id + ", pid=" + pid + ", name=" + name + "]";
    }
}

打印结果：

[{"id":"0001","pid":null,"name":"中国","children":[{"id":"0002","pid":"0001","name":"河北","children":[{"id":"0004","pid":"0002","name":"石家庄"}]},{"id":"0003","pid":"0001","name":"辽宁","children":[{"id":"0005","pid":"0003","name":"沈阳"}]}]},{"id":"0006","pid":null,"name":"美国","children":[{"id":"0007","pid":"0006","name":"纽约"}]}]

格式化结果：

[
    {
        "id": "0001",
        "pid": null,
        "name": "中国",
        "children": [
            {
                "id": "0002",
                "pid": "0001",
                "name": "河北",
                "children": [
                    {
                        "id": "0004",
                        "pid": "0002",
                        "name": "石家庄"
                    }
                ]
            },
            {
                "id": "0003",
                "pid": "0001",
                "name": "辽宁",
                "children": [
                    {
                        "id": "0005",
                        "pid": "0003",
                        "name": "沈阳"
                    }
                ]
            }
        ]
    },
    {
        "id": "0006",
        "pid": null,
        "name": "美国",
        "children": [
            {
                "id": "0007",
                "pid": "0006",
                "name": "纽约"
            }
        ]
    }
]

实际项目应用见：SMSE

为 easyui-tree