MySQL数据库事务实例（模拟银行转账）

在数据库系列文章中[MySQL数据库事务基本操作](http://blog.youkuaiyun.com/fengpojian/article/details/73571983)
介绍了MySQL数据库基本的事务操作。这篇文章将介绍一个实例来更好的理解学习MySQL数据库事务。
这个Demo主要是模拟银行转账的过程，两个账户发生转账关系时，首先改变双方账户的余额状态。
随后验证转出方账户是否有足够的余额来支撑此次的转账操作，若余额不足，则抛出“账户余额不足”异常。
请注意，这个Demo只适用于单线程的情况。

java
/**
 * 单线程下的数据库事务
 * 模拟银行转账
 * @author LinGer
 *
 */
public class Transaction
{
    public boolean transfrom(int fromId, int toId, double amount)
    {
        Connection con = MyUtil.getCon();
        String sql1 = "update tb_account set balance = balance - ? where userId = ?;";
        String sql2 = "update tb_account set balance = balance + ? where userId = ?;";
        String sql3 = "select balance  from tb_account where userId = ?;";
        PreparedStatement ps1 = null;
        PreparedStatement ps2 = null;
        PreparedStatement ps3 = null;
        ResultSet rs = null;
        try
        {
            //开启事务
            con.setAutoCommit(false);
            //转账时涉及的两个账户以及各账户的金额变动
            ps1 = con.prepareStatement(sql1);
            ps1.setDouble(1, amount);
            ps1.setInt(2, fromId);
            ps1.executeUpdate();

            ps2 = con.prepareStatement(sql2);
            ps2.setDouble(1, amount);
            ps2.setInt(2, toId);
            ps2.executeUpdate();

            //检查转出方账户的余额是否足够支持此次转账金额；如果余额不足，则抛出“余额不足”异常，并回滚
            ps3 = con.prepareStatement(sql3);
            ps3.setInt(1, fromId);
            rs = ps3.executeQuery();
            Double balance = 0.0;
            if(rs.next())
            {
                balance = rs.getDouble("balance");
            }
            if(balance < 0)
            {
                throw new Exception("账户余额不足");
            }
            con.commit();
            return true;
        } catch (Exception e)
        {
            e.printStackTrace();
        }
        try
        {
            con.rollback();
        } catch (SQLException e)
        {
            e.printStackTrace();
        }finally{
            try
            {
                rs.close();
                ps1.close();
                ps2.close();
                ps3.close();
                con.close();
            } catch (SQLException e)
            {
                e.printStackTrace();
            }
        }
        return false;
    }
}

java
/**
 * 工具类 获得Connection连接
 * @return
 */
public static Connection getCon()
    {
        String DBDriver = "com.mysql.jdbc.Driver";
        String DBUrl = "jdbc:mysql://localhost:3306/study?autoReconnect=true&"
                + "failOverReadOnly=false&useUnicode=true&characterEncoding=UTF-8";
        String name = "root";
        String pass = "123";
        Connection con = null;
        try {
            Class.forName(DBDriver);
            con = DriverManager.getConnection(DBUrl,name,pass);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return con;
    }

java
/**
 * 实体类 模拟银行账户
 * @author LinGer
 *
 */
public class User
{
    private int userId;
    private String userName;
    private Double balance; //账户余额

    //get && set
    public int getUserId()
    {
        return userId;
    }
    public void setUserId(int userId)
    {
        this.userId = userId;
    }
    public String getUserName()
    {
        return userName;
    }
    public void setUserName(String userName)
    {
        this.userName = userName;
    }
    public Double getBalance()
    {
        return balance;
    }
    public void setBalance(Double balance)
    {
        this.balance = balance;
    }
}

这篇博客的代码参考了https://www.oschina.net/code/snippet_2271303_44733#62843
非常感谢博主。