일단 하나를 해보자

Class.forName("org.mariadb.jdbc.Driver");

package util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.sql.DataSource;

public class DBManager {
    public static Connection getConnection(){


        Connection con = null;

        String server = "서버주소(나는 localhost)";
        String database = "데이터베이스 이름";
        String user_name = "유저네임";
        String password = "비밀번호";

        try {
            Class.forName("org.mariadb.jdbc.Driver");
            System.out.println("드라이브로드 성공");

        } catch (ClassNotFoundException e) {
            System.err.println(" 드라이버 로딩 오류 : " + e.getMessage());
            e.printStackTrace();
        }

        try {
            con = DriverManager.getConnection("jdbc:mariadb://" +
                    server + "/" +
                    database +
                    "?useSSL=false", user_name, password); // SSL 실행 확인
            System.out.println("연결 성공");
        } catch(Exception e) {
            System.err.println("에러 내용 :" + e.getMessage());
            e.printStackTrace();
        }

        System.out.println("con리턴" +con);
        return con;



    }
    //select 수행한 후 리소스 해제를 위한 메소드
    public static void close(Connection conn, Statement stmt, ResultSet rs){
        try{
            rs.close();
            stmt.close();
            conn.close();
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    //insert, update, delete 작업을 수행한 후 리소스 해제를 위한 메소드
    public static void close(Connection conn, Statement stmt){
        try{
            stmt.close();
            conn.close();
        } catch (Exception e){
            e.printStackTrace();
        }
    }
}

package com.saeyan.dao;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import util.DBManager;

import com.saeyan.dto.ProductVO;

public class ProductDAO {
    private ProductDAO(){

    }
    private static ProductDAO instance = new ProductDAO();
    public static ProductDAO getInstance(){
        return instance;
    }

    //c Read u d
    public  List<ProductVO> selectAllProducts(){
        //최근 등록한 상품 먼저 출력하기
        String sql= "select * from product order by code desc";
        List<ProductVO> list = new ArrayList<>();
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try{
            conn = DBManager.getConnection();
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();


            while (rs.next()){
                ProductVO pVo = new ProductVO();
                pVo.setCode(rs.getInt("code"));
                pVo.setName(rs.getString("name"));
                pVo.setPrice(rs.getInt("price"));
                pVo.setPictureUrl(rs.getString("pictureurl"));
                pVo.setDescription(rs.getString("description"));

                list.add(pVo); //앗 얘를 빼먹었었네!
            }


        } catch(Exception e){
            System.out.println("값 못가져옴:"+e.getMessage());


        } finally {
            DBManager.close(conn, pstmt, rs);
        }
        return list;
    }

}