将从数据库查询出来的带有父子结构的list转换成treeList结构

package test;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class DBHelper {
     public static final String url = "jdbc:mysql://127.0.0.1/peixian";
        public static final String name = "com.mysql.jdbc.Driver";
        public static final String user = "root";
        public static final String password = "root";
 
        public Connection conn = null;
        public PreparedStatement pst = null;  
 
        public  DBHelper(String sql) {
            try {
                Class.forName(name);//指定连接类型
                conn = DriverManager.getConnection(url,user,password);//获取连接
                pst = conn.prepareStatement(sql);//准备执行语句
            } catch (Exception e) {
                e.printStackTrace();
            }
        }  
 
        public void close() {
            try {
                this.conn.close();
                this.pst.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
 
}
//调用demo类================
package test;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import com.mysql.jdbc.StringUtils;
public class Demo {
    static String sql = null;
    static DBHelper db1 = null;
    static ResultSet ret = null;  
 
    public static void main(String[] args) {
        sql = "select *from xy_sys_menu";//SQL语句
        db1 = new DBHelper(sql);//创建DBHelper对象
 
        try {
            List<Map<String,Object>>list=new ArrayList<Map<String,Object>>();
            ret = db1.pst.executeQuery();//执行语句，得到结果集
            ResultSetMetaData md = ret.getMetaData(); //获得结果集结构信息,元数据
            int columnCount = md.getColumnCount();   //获得列数
            while (ret.next()) {
                Map<String,Object> rowData = new HashMap<String,Object>();
                for (int i = 1; i <= columnCount; i++) {
                    rowData.put(md.getColumnName(i), ret.getObject(i));
                }
                list.add(rowData);
 
            }
            System.out.println("list============="+list);
            List<Map<String, Object>>listTree=getTreeList("MENU_NO","PMENU_NO","children",list);
            System.out.println("listTree===="+listTree);
            ret.close();
            db1.close();//关闭连接
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
 
  //把带有父子机构的数据变成treelist形式
    public static List<Map<String, Object>> getTreeList(String id,String pid,String children,List<Map<String, Object>>list) {
    //List<Map<String, Object>>listmap=new ArrayList<Map<String, Object>>();
    //给list的每一项加一个子项
    for(int i=0;i<list.size();i++) {
     list.get(i).put(children, new ArrayList<Map<String, Object>>());
    }
    List<Map<String, Object>>treelist=new ArrayList<Map<String, Object>>();
    for(Map<String, Object> outmap:list) {
        for(Map<String, Object> inmap:list) {
            String outid=outmap.get(id).toString();
            String inpid=inmap.get(pid).toString();
            if(outid.equals(inpid)) {
            List<Map<String, Object>>maplist=(ArrayList) outmap.get(children);
            maplist.add(inmap);
            }
        }
        String prid=outmap.get(pid).toString();
        if(StringUtils.isNullOrEmpty(prid)) {
          treelist.add(outmap);
        }
    }
    return treelist;
    }
}