JDBC 加钱减钱

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

import cn.tedu.jdbc.day02.DbUtils;

public class Demo {

public static void main(String[] args) {
pay(3,1,1500);
System.out.println("Ok");

}
public static void pay(int from,int to,double money){
String sql1="update r_account set balance=balance+? where id=?";
String sql2="select balance from r_account where id=?";
Connection conn=null;
try {
conn=DbUtils.getConnection();
conn.setAutoCommit(false);
PreparedStatement ps=conn.prepareStatement(sql1);
//减钱
ps.setDouble(1, -money);
ps.setInt(2, from);
int n=ps.executeUpdate();
if(n!=1){
throw new Exception("扣错了");
}
//加钱
ps.setDouble(1, money);
ps.setInt(2, to);
n=ps.executeUpdate();
if(n!=1){
throw new Exception("加错了");
}
ps.close();
//检查
ps=conn.prepareStatement(sql2);
ps.setInt(1, from);
ResultSet rs=ps.executeQuery();
while(rs.next()){
double bal=rs.getDouble(1);
if(bal<0){
throw new Exception("透支了");
}
}

conn.commit();
} catch (Exception e) {
e.printStackTrace();
DbUtils.rollback(conn);
}finally {
DbUtils.close(conn);
}

}