递归查询森林结构所有子节点

朴灿烈づ我的快乐病毒、 2022-12-23 11:22 188阅读 0赞

一张表用来存储树形结构的父节点和叶子节点，大体是这样定义的。

测试数据  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podXlpbjY1NTM_size_16_color_FFFFFF_t_70_pic_center]

需求很简单：这张表表示的是一个数结构，其中groupid代表的是父节点，而nodeid代表的是相应的子节点，我们想要的是整个树结构的全部叶子节点。当然涉及到多棵树，就组成了森林结构，也就是查找指定森林结构的所有叶子节点。

思路也很Easy：遍历每一颗树，利用写好的递归查询函数去查询每棵树的最终叶子结点，然后把它们保存到静态list中。

import java.util.ArrayList;
    import java.util.List;
    import java.sql.*;
    
    public class FindLeaf { 
        /** * @param args */
    
        private static List<String>leaf = new ArrayList<String>();
    
        public static void main(String[] args) { 
    
            // TODO Auto-generated method stub
            
    
            FindLeaf test = new FindLeaf();
    
            List<String> list = new ArrayList<String>();
    
            list.add("A001");
    
            list.add("B001");
    
            list.add("C001");
    
            for (int i = 0; i < list.size(); i++) { 
                try { 
                    test.search (list.get(i).toString());
                } catch (Exception e) { 
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            System.out.println(leaf);
        }
            /* * 递归函数 * */
    
            public List<String> search (String args) throws Exception { 
    
                Connection con = createConnection();
    
                List<String> tmplist = new ArrayList<String>();
                /* 构建SQL*/
                String sql = "select nodeid from setnode where groupid = '" + args+ "'";
    
                /* * 判断是否为叶子节点 * */
    
                String sql2 = "select groupid from setnode where groupid = '" + args+ "'";
    
                //PreparedStatement ps = con.prepareStatement(sql2);
    
                ResultSet rs2 = con.prepareStatement(sql2).executeQuery();
    
                List<String> list2 = rs2list(rs2);
    
                if (list2.size() == 0) { 
    
                    con.close();
    
                    System.out.println("最终叶子节点是：" + args);
    
                    leaf.add(args);
    
                } else { 
    
                    ResultSet rs = con.prepareStatement(sql).executeQuery();
    
                    tmplist = rs2list(rs);
    
                    for (int i = 0; i < tmplist.size(); i++) { 
                        search(tmplist.get(i).toString()); //递归循环查询
    
                    }
                }
    
                if(con!=null){ 
                    con.close();
                }
                return leaf;
            }
    
            public Connection createConnection() { 
    
                Connection con = null;
    
                String url = "jdbc:postgresql://106.225.225.25:5432/postgres";
    
                String user = "postgres";
    
                String pass = "postgres";
    
                try { 
    
                    Class.forName("org.postgresql.Driver");
    
                    con = DriverManager.getConnection(url, user, pass);
    
                     System.out.println("Connection successfully established!");
    
                } catch (ClassNotFoundException e) { 
    
                    // TODO Auto-generated catch block
    
                    e.printStackTrace();
    
                } catch (SQLException e) { 
                    // TODO Auto-generated catch block
    
                    e.printStackTrace();
                }
                return con;
            }
    
            private static List<String> rs2list(ResultSet rs) throws SQLException {   //将结果集ResultSet转换为list
    
                // TODO Auto-generated method stub
    
                List<String> list = new ArrayList<String>();
    
                while (rs.next()) { 
                    list.add(rs.getString(1).trim());
                }System.out.println(list);
                return list;
            }
        }

输出:
    [A0010101, A0010102, B00101, B00102, C00101, C00102]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podXlpbjY1NTM_size_16_color_FFFFFF_t_70_pic_center]: /images/20221120/bb3e2f5ec8f542fe882a2ca7d5dcaa93.png