在千锋“逆战”学习第42天

      每日一句：编程中我们会遇到多少挫折？表放弃，沙漠尽头必是绿洲。
      今天学习了jdbc中的ResultSet结果集，常见错误，SQL注入问题和PreparedStatement接口。
      明天继续努力。

银行数据系统

public class TestMain {
    public static void main(String[] args) {
        AccountSystem as = new AccountSystem();
        Scanner scanner = new Scanner(System.in);
        System.out.println("-----欢迎来到银行系统-----");
        int choice = 0;
        do{
            System.out.println("1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出");
            System.out.println("请选择");
            choice = scanner.nextInt();
            switch (choice){
                case 1:
                    as.regiter();
                    break;
                case 2:
                    as.saveMoney();
                    break;
                case 3:
                    as.takeMoney();
                    break;
                case 4:
                    as.transferAccount();
                    break;
                case 5:
                    as.alterPassword();
                    break;
                case 6:
                    as.delete();
                    break;
                case 0:
                    as.closeConnection();
                    return;
            }
        }while(choice!=0);
    }
}

public class AccountSystem {
    Scanner scanner = new Scanner(System.in);
    private static Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;

    static {
        //重复的操作，就触发一次加载！
        try {
            //1. 加载驱动
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/account?useUnicode=true&characterEncoding=utf8", "root", "123456");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    //开户
    public void regiter() {
        System.out.print("卡号：");
        String cardId = scanner.next();
        System.out.print("密码：");
        String password = scanner.next();
        System.out.print("用户名：");
        String username = scanner.next();
        System.out.print("存款金额：");
        double balance = scanner.nextDouble();
        System.out.print("手机号码：");
        String phone = scanner.next();

        try {
            //3.创建PreparedStatement
            String sql = "insert into t_account(cardId,password,username,balance,phone) values (?,?,?,?,?)";
            preparedStatement = connection.prepareStatement(sql);
            //4.为占位符赋值
            preparedStatement.setString(1, cardId);
            preparedStatement.setString(2, password);
            preparedStatement.setString(3, username);
            preparedStatement.setDouble(4, balance);
            preparedStatement.setString(5, phone);
            //5.执行SQL语句
            int i = preparedStatement.executeUpdate();
            //6.处理结果
            if (i > 0) {
                System.out.println("开户成功！");
            } else {
                System.out.println("开户失败！");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (preparedStatement != null) {
                    preparedStatement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    //存款
    public void saveMoney() {
        System.out.print("请输入卡号：");
        String cardId = scanner.next();
        System.out.print("请输入密码:");
        String password = scanner.next();
        System.out.print("请输入存款金额");
        double money = scanner.nextDouble();
        if (money > 0) {
            //存款操作
            String sql = "update t_account set balance = balance + ? where cardId=? and password=?";
            try {
                //预编译
                preparedStatement = connection.prepareStatement(sql);
                preparedStatement.setDouble(1, money);
                preparedStatement.setString(2, cardId);
                preparedStatement.setString(3, password);
                //执行 接收返回结果
                int i = preparedStatement.executeUpdate();
                if (i > 0) {
                    System.out.println("存款成功！");
                } else {
                    System.out.println("存款失败！请核对用户名或密码！");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (preparedStatement != null) {
                        preparedStatement.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        } else {
            System.out.println("您输入的金额不正确！");
        }
    }

    //取款
    public void takeMoney() {
        System.out.print("卡号：");
        String cardId = scanner.next();
        System.out.print("密码:");
        String password = scanner.next();
        System.out.print("取款金额");
        double money = scanner.nextDouble();
        if (money > 0) {
            //取款操作
            //1.先查询cardId和password对应的数据，余额
            String sql = "select balance from t_account where cardId=? and password= ?";
            try {
                preparedStatement = connection.prepareStatement(sql);
                preparedStatement.setString(1, cardId);
                preparedStatement.setString(2, password);
                resultSet = preparedStatement.executeQuery();
                if (resultSet.next()) {//得到的是单行单列的数据
                    double balance = resultSet.getDouble(1);
                    if (money <= balance) {
                        //取款操作！
                        String sql2 = "update t_account set balance = balance - ? where cardId=? and password= ?";
                        preparedStatement = connection.prepareStatement(sql2);
                        preparedStatement.setDouble(1, money);
                        preparedStatement.setString(2, cardId);
                        preparedStatement.setString(3, password);
                        int i = preparedStatement.executeUpdate();
                        if (i > 0) {
                            System.out.println("取款成功！");
                        }
                    } else {
                        System.out.println("余额不足！");
                    }
                } else {
                    System.out.println("请核实用户名或密码！");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (resultSet != null) {
                        resultSet.close();
                    }
                    if (preparedStatement != null) {
                        preparedStatement.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        } else {
            System.out.println("金额不正确！");
        }
    }

    //转账
    public void transferAccount() {
        System.out.print("卡号：");
        String cardId1 = scanner.next();
        System.out.print("密码:");
        String password = scanner.next();
        System.out.print("转账金额：");
        Double money = scanner.nextDouble();
        System.out.print("被转账人卡号：");
        String cardId2 = scanner.next();
        if (money > 0) {
            String sql1 = "select balance from t_account where cardId=? and password= ?";
            try {
                preparedStatement = connection.prepareStatement(sql1);
                preparedStatement.setString(1, cardId1);
                preparedStatement.setString(2, password);
                resultSet = preparedStatement.executeQuery();
                if (resultSet.next()) {
                    double balance = resultSet.getDouble(1);
                    if (money <= balance) {
                        //转账操作
                        String sql2 = "update t_account set balance = balance - ? where cardId=? and password= ?";
                        preparedStatement = connection.prepareStatement(sql2);
                        preparedStatement.setDouble(1, money);
                        preparedStatement.setString(2, cardId1);
                        preparedStatement.setString(3, password);
                        int i1 = preparedStatement.executeUpdate();
                        //收款操作
                        String sql3 = "update t_account set balance = balance + ? where cardId = ?";
                        preparedStatement = connection.prepareStatement(sql3);
                        preparedStatement.setDouble(1, money);
                        preparedStatement.setString(2, cardId2);
                        int i2 = preparedStatement.executeUpdate();
                        if (i1 > 0 && i2 > 0) {
                            System.out.println("转账成功");
                        }
                    } else {
                        System.out.println("余额不足，转账失败！");
                    }
                } else {
                    System.out.println("请核实用户名或密码！");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (resultSet != null) {
                        resultSet.close();
                    }
                    if (preparedStatement != null) {
                        preparedStatement.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        } else {
            System.out.println("输入金额错误");
        }
    }

    //修改密码
    public void alterPassword() {
        System.out.print("卡号：");
        String cardId = scanner.next();
        System.out.print("密码:");
        String password = scanner.next();
        System.out.print("新密码：");
        String newPassword = scanner.next();
        String sql = "update t_account set password = ? where cardId = ?";
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, newPassword);
            preparedStatement.setString(2, cardId);
            int i = preparedStatement.executeUpdate();
            if (i > 0) {
                System.out.println("修改成功");
            } else {
                System.out.println("修改失败");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (resultSet != null) {
                    resultSet.close();
                }
                if (preparedStatement != null) {
                    preparedStatement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    //注销
    public void delete() {
        System.out.print("注销卡号：");
        String cardId = scanner.next();
        System.out.print("密码:");
        String password = scanner.next();
        String sql = "delete from t_account where cardId = ? and password = ?";
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, cardId);
            preparedStatement.setString(2, password);
            int i = preparedStatement.executeUpdate();
            if (i > 0) {
                System.out.println("注销成功！");
            } else {
                System.out.println("注销失败！");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (resultSet != null) {
                    resultSet.close();
                }
                if (preparedStatement != null) {
                    preparedStatement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    //只服务关闭！
    public void closeConnection() {
        try {
            if (connection != null) {
                connection.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

-----欢迎来到银行系统-----
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
1
卡号：202003302130
密码：123456
用户名：barry
存款金额：8000
手机号码：13947581632
开户成功！
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
2
请输入卡号：202003302130
请输入密码:123456
请输入存款金额2000
存款成功！
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
3
卡号：202003302130
密码:123456
取款金额4000
取款成功！
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
4
卡号：202003302050
密码:123456
转账金额：5000
被转账人卡号：202003302130
转账成功
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
5
卡号：202003302130
密码:123456
新密码：1234
修改成功
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
6
注销卡号：202003302130
密码:1234
注销成功！
1、开户 2、存款 3、取款 4、转账 5、修改密码 6、注销 0、退出
请选择
0