银行转账案例演示

1.需求：一个账号fromAccount向另一个账号toAccount转入money元钱
2.分析：

• 检查两个账号是否存在，不存在的话，结束转账行为
• 检查转出账号的里金额是否充足，不充足，结束转账行为,充足的话，进行扣款money元
• 转入账号进行增加money元
  3.数据准备参考上一篇
  https://www.cnblogs.com/dch-21/p/12920178.html

<code>public class Test {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入出账账号:");
        String fromAccount=scanner.nextLine();
        System.out.println("请输入进账账号:");
        String toAccount=scanner.nextLine();
        System.out.println("请输入转账金额:");
        double money=scanner.nextDouble();
        oneToOne(fromAccount,toAccount,money);
    }
    public static void oneToOne(String fromAccount,String toAccount,double money){
        if(fromAccount==null||fromAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(toAccount==null||toAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(money<0){
            System.out.println("输入不正确");
            return;
        }
        Connection connection=null;
        PreparedStatement ps=null;
        ResultSet resultSet=null;
        try{
            connection= DBUtil.getConnection();
            String sql="select * from bank_account where account_id=?";
            ps=connection.prepareStatement(sql);
            ps.setString(1,fromAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("出账账号有误");
                return;
            }
            double balance = resultSet.getDouble("account_balance");
            ps=connection.prepareStatement(sql);
            ps.setString(1,toAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("进账账号有误");
                return;
            }
            String sql1="update bank_account set account_balance=account_balance+? where account_id=?";
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,-money);
            ps.setString(2,fromAccount);
            int i = ps.executeUpdate();
            System.out.println(i+"条数据受到影响");
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,money);
            ps.setString(2,toAccount);
            int j = ps.executeUpdate();
            System.out.println(j+"条数据受到影响");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            DBUtil.closeConnection(connection,ps,resultSet);
        }
    }
}
</code>

输入

运行前

运行后

转账异常演示

在转出账户转出金额之后和转入账户收入金额之前模拟空指针异常
String str = null;
System.out.println(str.length());

<code>package practice;
import practice.jdbc.day03.DBUtil;
import java.io.InputStream;
import java.sql.*;
import java.util.Objects;
import java.util.Properties;
import java.util.Scanner;
/**
 * @Author 昊
 * @Create 2020/5/19 21:29
 * @Description
 *
 * 模拟银行一对一转账
 */
public class Test {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入出账账号:");
        String fromAccount=scanner.nextLine();
        System.out.println("请输入进账账号:");
        String toAccount=scanner.nextLine();
        System.out.println("请输入转账金额:");
        double money=scanner.nextDouble();
        oneToOne(fromAccount,toAccount,money);
    }
    public static void oneToOne(String fromAccount,String toAccount,double money){
        if(fromAccount==null||fromAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(toAccount==null||toAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(money<0){
            System.out.println("输入不正确");
            return;
        }
        Connection connection=null;
        PreparedStatement ps=null;
        ResultSet resultSet=null;
        try{
            connection= DBUtil.getConnection();
            String sql="select * from bank_account where account_id=?";
            ps=connection.prepareStatement(sql);
            ps.setString(1,fromAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("出账账号有误");
                return;
            }
            double balance = resultSet.getDouble("account_balance");
            ps=connection.prepareStatement(sql);
            ps.setString(1,toAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("进账账号有误");
                return;
            }
            String sql1="update bank_account set account_balance=account_balance+? where account_id=?";
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,-money);
            ps.setString(2,fromAccount);
            int i = ps.executeUpdate();
            System.out.println(i+"条数据受到影响");
            //在转出账户转出金额之后和转入账户收入金额之前模拟空指针异常
            String str = null;
            System.out.println(str.length());
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,money);
            ps.setString(2,toAccount);
            int j = ps.executeUpdate();
            System.out.println(j+"条数据受到影响");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            DBUtil.closeConnection(connection,ps,resultSet);
        }
    }
}
</code>

加入空指针异常前

加入异常后

解决方案

将手动提交事务改为自动提交，并设置回滚
setAutoCommit(false);
取消事务的自动提交操作，变成手动提交；默认为自动提交；true为自动提交，fals为手动提交
rollback();回滚到事务之初
releaseSavepoint(Savepoint savepoint);回滚到指定位置

事务

事务的特点：

• 默认情况下，MySQL每执行一条SQL语句，都是一个单独的事务。
• 如果需要在一个事务中包含多条SQL语句，那么需要开启事务和结束事务。
  • 开启事务：start transaction；
  • 结束事务：commit或rollback；

jdbc的事务支持

Connection.setAutoCommit(boolean flag):此方法可以取消事务的自动提交功能，值为false。
Connection.commit()：进行事务提交 。
Connection.rollback():进行事务回滚。

<code>public class Test {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入出账账号:");
        String fromAccount=scanner.nextLine();
        System.out.println("请输入进账账号:");
        String toAccount=scanner.nextLine();
        System.out.println("请输入转账金额:");
        double money=scanner.nextDouble();
        oneToOne(fromAccount,toAccount,money);
    }
    public static void oneToOne(String fromAccount,String toAccount,double money){
        if(fromAccount==null||fromAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(toAccount==null||toAccount.length()==0){
            System.out.println("输入不正确");
            return;
        }
        if(money<0){
            System.out.println("输入不正确");
            return;
        }
        Connection connection=null;
        PreparedStatement ps=null;
        ResultSet resultSet=null;
        try{
            connection= DBUtil.getConnection();
            //取消事务的自动提交操作，变成手动提交
            //默认为自动提交
            //true为自动提交，fals为手动提交
            connection.setAutoCommit(false);
            String sql="select * from bank_account where account_id=?";
            ps=connection.prepareStatement(sql);
            ps.setString(1,fromAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("出账账号有误");
                return;
            }
            double balance = resultSet.getDouble("account_balance");
            ps=connection.prepareStatement(sql);
            ps.setString(1,toAccount);
            resultSet = ps.executeQuery();
            if(!resultSet.next()){
                System.out.println("进账账号有误");
                return;
            }
            String sql1="update bank_account set account_balance=account_balance+? where account_id=?";
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,-money);
            ps.setString(2,fromAccount);
            ps.executeUpdate();
           
            //在转出账户转出金额之后和转入账户收入金额之前模拟空指针异常
            String str = null;
            System.out.println(str.length());
            ps=connection.prepareStatement(sql1);
            ps.setDouble(1,money);
            ps.setString(2,toAccount);
            ps.executeUpdate();
           
        }catch (Exception e){
            e.printStackTrace();
            //如果中途出现异常，会回滚到事务之初
            try {
                connection.rollback();
            } catch (SQLException ex) {
                ex.printStackTrace();
            }
        }finally {
            DBUtil.closeConnection(connection,ps,resultSet);
        }
    }
}
</code>

JDBC（三）——事务

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