使用递归算法结合数据库解析成Java树形结构的代码解析

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
}

总结

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