有两个类：BaseDao是数据库连接类。AlbumDaoImpl类继承了BaseDao，实现了一个AlbumDao接口。在BaseDao中调用函数executeQuery（）是返回正常的ResultSet，但是在AlbumDaoImpl类中调用后返回的ResultSet对象时空的！！！
这个是BaseDao中的函数

 

    public ResultSet executeQuery(String sql,Object []params){
                rs=null;
                
                if(conn==null){
                    conn=getConnection();
                }
                else{
                    try {
                        presta=conn.prepareStatement(sql);
                        if(params!=null && params.length>0){
                            for(int i=0;i<params.length;i++){
                                presta.setObject(i+1, params[i]);
                            }
                        }
                        rs=presta.executeQuery();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }            
                }        
                
                return rs;
            }

这个是AlbumDaoImpl中的一个方法：

    public void getAlbumList() {
            String sql="select * from album";
            Object []params={};
            ResultSet res=null;
            res=this.executeQuery(sql,params);
            System.out.println(res);
            try {
                while(res.next()){
                    int id=res.getInt("id");
                    String artist =res.getString("Artist");
                    String title =res.getString("Title");
                    double price = res.getDouble("Price");
                    Date dateReleased = res.getDate("DateReleased");
                    String description = res.getString("Description");
                    System.out.println(id+"\t"+artist+"\t"+title+"\t"+price+"\t"+dateReleased+"\t"+description);                
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            finally{
                this.closeResource();
            }
        }

一直报空指针异常！！！

在BaseDao中用同样的代码测试是有结果集的！！

    public static void main(String[] args) {
            Connection con=null;
            BaseDao test=new BaseDao();
            con=test.getConnection();
            String sql="select * from album";
            Object []params={};
            ResultSet rs=null;
            rs=test.executeQuery(sql,params);
            System.out.println(rs);
            try {
                while(rs.next()){
                    int id=rs.getInt("id");
                    String artist =rs.getString("Artist");
                    String title =rs.getString("Title");
                    double price = rs.getDouble("Price");
                    Date dateReleased = rs.getDate("DateReleased");
                    String description = rs.getString("Description");
                    System.out.println(id+"\t"+artist+"\t"+title+"\t"+price+"\t"+dateReleased+"\t"+description);                
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            finally{
                test.closeResource();
            }
        }

求解为什么？