递归查询森林结构所有子节点

近期工作上遇到了这样一个需求，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。

Table定义如下：

id	groupid	nodeid	other
1	A001	A0001	~~
2	B001	B0001	~~
3	A0001	A00001	~~
4	C001	C0001	~~
5	C001	C0002	~~

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。

详细代码如下：

package org.uugu.test; 

import java.util.ArrayList;
import java.util.List;
import java.sql.*; 

public class FindLeaf {
                /**

                * @param args

                */

                private static List&lt;String&gt; leaf = new ArrayList&lt;String&gt;(); 

                public static void main(String[] args) {

                                // TODO Auto-generated method stub                                

                                FindLeaf test = new FindLeaf();

                                List&lt;String&gt; list = new ArrayList&lt;String&gt;();

                                list.add("A001");

                                list.add("B001");

                                for (int i = 0; i &lt; 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&lt;String&gt; search(String args) throws Exception {

                                Connection con = createConnection();

                                List&lt;String&gt; tmplist = new ArrayList&lt;String&gt;(); /*  * 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&lt;String&gt; 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 &lt; 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://localhost:5432/postgres";

                                String user = "postgres";

                                String pass = "123";

                                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&lt;String&gt; rs2list(ResultSet rs) throws SQLException {  //将结果集ResultSet转换为list

                                // TODO Auto-generated method stub

                                List&lt;String&gt; list = new ArrayList&lt;String&gt;();

                                while (rs.next()) {
                                                list.add(rs.getString(1).trim());
                                }
                                // System.out.println(list);
                                return list;
                }
}

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package org.uugu.test;

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");

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://localhost:5432/postgres";

String user = "postgres";

String pass = "123";

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;

}

指定结果为：leaf[‘A00001′,’B0001’]

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递归查询森林结构所有子节点

《递归查询森林结构所有子节点》有一个想法