javaweb中dao层如何使用

项目具体目录如下：

Basedao的内容如下：

package com.monkeyshop.dao;import java.sql.*;public class Basedao {static{//加载驱动 mysql8.0及以上版本加载方式try {Class.forName("com.mysql.cj.jdbc.Driver");} catch (ClassNotFoundException e) {e.printStackTrace();}}//都声明为静态方法是为了防止出错public static Connection getconn(){//创建一个链接对象Connection conn = null;try {//monkeyshop 数据库名                           用户名   密码  其余的内容差不多是固定的conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/monkeyshop?useSSL=false&serverTimezone=UTC","root","root");} catch (SQLException e) {e.printStackTrace();}return  conn;}public static  int exectuIUD(String sql,Object[] params){int count = 0;//获取连接对象Connection conn = Basedao.getconn();//准备SQLPreparedStatement ps= null;try {ps = conn.prepareStatement(sql);for(int i=0; i<params.length; i++){ps.setObject(i+1,params[i]);}count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();}finally {Basedao.closeall(null,ps,conn); //释放资源吧  结果集 声明 连接}return  count;}public static void closeall(ResultSet rs,PreparedStatement ps, Connection conn){try {if(rs != null)rs.close();if(ps!=null){ps.close();}if(conn!=null)conn.close();} catch (SQLException e) {e.printStackTrace();}}
}

sevice层例如购物车代码

package com.monkeyshop.service;import com.monkeyshop.dao.Basedao;
import com.monkeyshop.entity.MONKEY_CART;
import com.monkeyshop.entity.MONKEY_PRODUCT;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collections;public class MONKEY_CARTDao {public static int insert(MONKEY_CART cart) {String sql = "insert into lmonkey_cart values(null,?,?,?,?,?,?,?,?)";Object[] params = {cart.getCart_p_filename(),cart.getCart_p_name(),cart.getCart_p_price(),cart.getCart_quantity(),cart.getCart_p_stock(),cart.getCart_p_id(),cart.getCart_u_id(),cart.getCart_valid()};return  Basedao.exectuIUD(sql,params);}public static ArrayList<MONKEY_CART> getCart(String uid) {ArrayList<MONKEY_CART> shoplist = new ArrayList<MONKEY_CART>();ResultSet rs = null;Connection conn = Basedao.getconn();PreparedStatement ps = null;String sql = "select * from lmonkey_cart where cart_u_id=? and cart_valid=1 order by cart_id desc";try {ps = conn.prepareStatement(sql);ps.setString(1,uid);rs = ps.executeQuery();while (rs.next()){MONKEY_CART c = new MONKEY_CART(rs.getInt("cart_id"),rs.getString("cart_p_filename"),rs.getString("cart_p_name"),rs.getInt("cart_p_price"),rs.getInt("cart_quantity"),rs.getInt("cart_p_stock"),rs.getInt("cart_p_id"),rs.getString("cart_u_id"),rs.getInt("cart_valid"));shoplist.add(c);}} catch (SQLException e) {e.printStackTrace();}finally {Basedao.closeall(rs,ps,conn);}return shoplist;}public static MONKEY_CART getCartShop(String uid, String pid) {MONKEY_CART c = null;ResultSet rs = null;Connection conn = Basedao.getconn();PreparedStatement ps = null;String sql = "select * from lmonkey_cart where cart_u_id=? and cart_p_id=? and cart_valid=1 order by cart_id desc";try {ps = conn.prepareStatement(sql);ps.setString(1,uid);ps.setInt(2,Integer.parseInt(pid));rs = ps.executeQuery();while (rs.next()){c = new MONKEY_CART(rs.getInt("cart_id"),rs.getString("cart_p_filename"),rs.getString("cart_p_name"),rs.getInt("cart_p_price"),rs.getInt("cart_quantity"),rs.getInt("cart_p_stock"),rs.getInt("cart_p_id"),rs.getString("cart_u_id"),rs.getInt("cart_valid"));}} catch (SQLException e) {e.printStackTrace();}finally {Basedao.closeall(rs,ps,conn);}return c;}public static MONKEY_CART getCartShop(String id) {MONKEY_CART c = null;ResultSet rs = null;Connection conn = Basedao.getconn();PreparedStatement ps = null;String sql = "select * from lmonkey_cart where cart_id=? and cart_valid=1 order by cart_id desc";try {ps = conn.prepareStatement(sql);ps.setString(1,id);rs = ps.executeQuery();while (rs.next()){c = new MONKEY_CART(rs.getInt("cart_id"),rs.getString("cart_p_filename"),rs.getString("cart_p_name"),rs.getInt("cart_p_price"),rs.getInt("cart_quantity"),rs.getInt("cart_p_stock"),rs.getInt("cart_p_id"),rs.getString("cart_u_id"),rs.getInt("cart_valid"));}} catch (SQLException e) {e.printStackTrace();}finally {Basedao.closeall(rs,ps,conn);}return c;}public static int updatenum(int cart_id, int countnew) {String sql = "update lmonkey_cart set cart_quantity=? where cart_id=?";Object[] params ={countnew,cart_id};return Basedao.exectuIUD(sql,params);}public static int getDeleteDD(int id) {String sql = "delete from lmonkey_cart where cart_id=?";Object[] params = {id};return Basedao.exectuIUD(sql,params);}
}

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