How to use recursive algorithms and code analysis to parse the database into a Java tree structure

This article mainly introduces the relevant information of code parsing using recursive algorithm combined with database parsing into Java tree structure. Friends in need can refer to the following

1. Prepare table structure And the corresponding table data

a, table structure:

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

b, table data:

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 object, corresponding to 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. Test data

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;
}
}

The output json format is as follows:

{
  "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
}

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