老师来康康

package common;

import java.sql.*;

public class DbUtils {
/**
     * 创建新的数据库连接
     * @return 新的Connection对象
     * @throws ClassNotFoundException
     * @throws SQLException
     */
    public static Connection getConnection() throws ClassNotFoundException, SQLException {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/imooc?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true", "root", "123456");
return conn;
    }

/**
     * 关闭连接，释放资源
     * @param rs 结果集对象
     * @param stmt Statement对象
     * @param conn Connection对象
     */
    public static  void closeConnection(ResultSet rs, Statement stmt, Connection conn){
try {
if(rs!=null){
                rs.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
try {
if(stmt != null){
                stmt.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
try {
if(conn != null && !conn.isClosed() ) {//conn.isClosed() == false
                conn.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
}
==============================================
package goodsapp.command;

import common.DbUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class InsertCommand implements Command{
    @Override
    public void execute() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            String sql = "insert into goods(name,price,desp) values(?,?,?)";
            conn = DbUtils.getConnection();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "耳机");
            pstmt.setFloat(2, 200);
            pstmt.setString(3,"蓝牙耳机");
            int cnt = pstmt.executeUpdate();
            if(cnt==1){
                System.out.println("添加成功");
                pstmt = conn.prepareStatement("select * from goods");
                rs = pstmt.executeQuery();
                while (rs.next()){
                    Integer id = rs.getInt(1);
                    String name = rs.getString("name");
                    Float price = rs.getFloat("price");
                    String desp = rs.getString("desp");
                    System.out.println(id+" "+name+" "+price+" "+desp);
                }
            }else{
                System.out.println("添加失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            DbUtils.closeConnection(rs,pstmt,conn);
        }
    }
}
==============================================
package goodsapp.command;

import common.DbUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class UpdateCommand implements Command {
    @Override
    public void execute() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            String sql = "update goods set price=? where name=?";
            conn = DbUtils.getConnection();
            pstmt = conn.prepareStatement(sql);
            pstmt.setFloat(1,1999);
            pstmt.setString(2, "手机");
            int cnt = pstmt.executeUpdate();
            if(cnt!=0){
                System.out.println("修改成功");
                pstmt = conn.prepareStatement("select * from goods");
                rs = pstmt.executeQuery();
                while (rs.next()){
                    Integer id = rs.getInt(1);
                    String name = rs.getString("name");
                    Float price = rs.getFloat("price");
                    String desp = rs.getString("desp");
                    System.out.println(id+" "+name+" "+price+" "+desp);
                }
            }else{
                System.out.println("修改失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            DbUtils.closeConnection(rs,pstmt,conn);
        }
    }
}
==================================================
package goodsapp.command;

import common.DbUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DeleteCommand implements Command{
    @Override
    public void execute() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            String sql = "delete from goods where name=?";
            conn = DbUtils.getConnection();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "耳机");
            int cnt = pstmt.executeUpdate();
            if(cnt!=0){
                System.out.println("删除成功");
                pstmt = conn.prepareStatement("select * from goods");
                rs = pstmt.executeQuery();
                while (rs.next()){
                    Integer id = rs.getInt(1);
                    String name = rs.getString("name");
                    Float price = rs.getFloat("price");
                    String desp = rs.getString("desp");
                    System.out.println(id+" "+name+" "+price+" "+desp);
                }
            }else{
                System.out.println("删除失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            DbUtils.closeConnection(rs,pstmt,conn);
        }
    }
}