1、准备表结构及对应的表数据
a、表结构：

create table TB_TREE
(
CID NUMBER not null,
CNAME VARCHAR2(50),
PID NUMBER //父节点
)

b、表数据：

insert into tb_tree (CID, CNAME, PID) values (1, '中国', 0);
insert into tb_tree (CID, CNAME, PID) values (2, '北京市', 1);
insert into tb_tree (CID, CNAME, PID) values (3, '广东省', 1);
insert into tb_tree (CID, CNAME, PID) values (4, '上海市', 1);
insert into tb_tree (CID, CNAME, PID) values (5, '广州市', 3);
insert into tb_tree (CID, CNAME, PID) values (6, '深圳市', 3);
insert into tb_tree (CID, CNAME, PID) values (7, '海珠区', 5);
insert into tb_tree (CID, CNAME, PID) values (8, '天河区', 5);
insert into tb_tree (CID, CNAME, PID) values (9, '福田区', 6);
insert into tb_tree (CID, CNAME, PID) values (10, '南山区', 6);
insert into tb_tree (CID, CNAME, PID) values (11, '密云县', 2);
insert into tb_tree (CID, CNAME, PID) values (12, '浦东', 4);

2、TreeNode对象，对应tb_tree

public class TreeNode implements Serializable {
private Integer cid;
private String cname;
private Integer pid;
private List nodes = new ArrayList();
 
public TreeNode() {
}
 
//getter、setter省略
}

3、测试数据

public class TreeNodeTest {
@Test
public void loadTree() throws Exception{
System.out.println(JsonUtils.javaToJson(recursiveTree(1)));
}
 
/**
* 递归算法解析成树形结构
*
* @param cid
* @return
* @author jiqinlin
*/
public TreeNode recursiveTree(int cid) {
//根据cid获取节点对象(SELECT * FROM tb_tree t WHERE t.cid=?)
TreeNode node = personService.getreeNode(cid);
//查询cid下的所有子节点(SELECT * FROM tb_tree t WHERE t.pid=?)
List childTreeNodes = personService.queryTreeNode(cid); 
//遍历子节点
for(TreeNode child : childTreeNodes){
TreeNode n = recursiveTree(child.getCid()); //递归
node.getNodes().add(n);
}
 
return node;
}
}

输出的json格式如下：

{
    "cid": 1,
    "nodes": [
        {
            "cid": 2,
            "nodes": [
                {
                    "cid": 11,
                    "nodes": [
                         
                    ],
                    "cname": "密云县",
                    "pid": 2
                }
            ],
            "cname": "北京市",
            "pid": 1
        },
        {
            "cid": 3,
            "nodes": [
                {
                    "cid": 5,
                    "nodes": [
                        {
                            "cid": 7,
                            "nodes": [
                                 
                            ],
                            "cname": "海珠区",
                            "pid": 5
                        },
                        {
                            "cid": 8,
                            "nodes": [
                                 
                            ],
                            "cname": "天河区",
                            "pid": 5
                        }
                    ],
                    "cname": "广州市",
                    "pid": 3
                },
                {
                    "cid": 6,
                    "nodes": [
                        {
                            "cid": 9,
                            "nodes": [
                                 
                            ],
                            "cname": "福田区",
                            "pid": 6
                        },
                        {
                            "cid": 10,
                            "nodes": [
                                 
                            ],
                            "cname": "南山区",
                            "pid": 6
                        }
                    ],
                    "cname": "深圳市",
                    "pid": 3
                }
            ],
            "cname": "广东省",
            "pid": 1
        },
        {
            "cid": 4,
            "nodes": [
                {
                    "cid": 12,
                    "nodes": [
                         
                    ],
                    "cname": "浦东",
                    "pid": 4
                }
            ],
            "cname": "上海市",
            "pid": 1
        }
    ],
    "cname": "中国",
    "pid": 0
}