用ThreadLocal完成事务:一个事务一次连接

ThreadLocal 线程变量,和Synchonized都用于处理多线程并发问题.

一句话理解ThreadLocal，向ThreadLocal里面存东西就是向它里面的Map存东西的，然后ThreadLocal把这个Map挂到当前的线程底下，这样Map就只属于这个线程了。

区别在于:ThreadLocal用数据隔离

                Synchonized用数据共享

思路:用set()方法将连接对象放入ThreadLocal中,使用时就通过get()方法拿出来.

//将连接存入ThreadLocal中

public static Connection getConnection(){
        Connection connection = threadLocal.get();
        if (connection!=null){
            return connection;
        }
        try{
            connection=JdbcUtils.getConnection();
            threadLocal.set(connection);
        }catch (Exception e){
            e.printStackTrace();
        }

        return threadLocal.get();
    }

//在service层调用



public void transfer(Integer sourceId, Integer targetId, Double money) {
        Connection connection = getConnection();


        try {
            connection.setAutoCommit(false);

            Account sourceAccount =  accountDao.findAccountById(sourceId,connection);
            Account targetAccount =  accountDao.findAccountById(targetId,connection);

            sourceAccount.setMoney(sourceAccount.getMoney()-money);
            accountDao.updateAccount(sourceAccount,connection);

            targetAccount.setMoney(targetAccount.getMoney()-money);
            accountDao.updateAccount(targetAccount,connection);


            connection.commit();
        }catch (Exception e){
            e.printStackTrace();

            try {
                connection.rollback();
            } catch (SQLException ex) {
                ex.printStackTrace();
            }
        }


    }