转账示例（三）：service层面实现（线程管理Connection）（本例采用QueryRunner来执行sql语句，数据源为C3P0）

缺点：Service层面还是不应该出现关于事务的操作

1.自行创建C3P0Uti，account数据库，导入Jar包

2.Dao层面

接口：

package com.learning.dao;

import com.learning.domain.Account;

public interface AccountDao {
    /**
     * 转账
     * @param fromname 转出用户
     * @param toname  转入用户
     * @param money  转账金额
     */
    @Deprecated
    public void updateAccount(String fromname,String toname,double money)throws Exception;

    /**
     * 根据账户信息修改金额
     * @param accout
     */
    public void updateAccout(Account accout) throws Exception;

    /**
     * 根据用户名查找账户信息
     * @param name
     * @return
     * @throws Exception
     */
    public Account findAccountByName(String name)throws Exception;
}

实现类：

package com.learning.dao.impl;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import com.learning.dao.AccountDao;
import com.learning.domain.Account;
import com.learning.util.C3P0Util;

public class AccountDaoImpl implements AccountDao {

    private Connection conn;

    public AccountDaoImpl(Connection conn) {
        this.conn = conn;
    }

    public void updateAccount(String fromname, String toname, double money) throws Exception {
        //创建一个QueryRunner对象
        QueryRunner qr = new QueryRunner(C3P0Util.getDataSource());
        qr.update("update account set money=money-? where name=?",money,fromname);
        qr.update("update account set money=money+? where name=?",money,toname);
    }

    public void updateAccout(Account account) throws Exception {
        QueryRunner qr = new QueryRunner();
        qr.update(conn,"update account set money=? where name=?",account.getMoney(),account.getName());
    }

    public Account findAccountByName(String name) throws Exception {
        QueryRunner qr = new QueryRunner();
        return qr.query(conn,"select * from account where name=?", new BeanHandler<Account>(Account.class),name);
    }

}

3.Service层面

接口：

package com.learning.service;

public interface AccountService {
    /**
     * 转账
     * @param fromname 转出用户
     * @param toname  转入用户
     * @param money  转账金额
     */
    public void transfer(String fromname,String toname,double money);
}

实现类：

package com.learning.service.impl;

import java.sql.Connection;
import java.sql.SQLException;

import com.learning.dao.AccountDao;
import com.learning.dao.impl.AccountDaoImpl;
import com.learning.domain.Account;
import com.learning.service.AccountService;
import com.learning.util.C3P0Util;
import com.learning.util.ManagerThreadLocal;

public class AccountServiceImpl implements AccountService {

    public void transfer(String fromname, String toname, double money) {
    //    ad.updateAccount(fromname, toname, money);
        AccountDao ad = new AccountDaoImpl();

        try {
            ManagerThreadLocal.startTransacation();//begin
            //分别得到转出和转入账户对象
            Account fromAccount = ad.findAccountByName(fromname);
            Account toAccount = ad.findAccountByName(toname);

            //修改账户各自的金额
            fromAccount.setMoney(fromAccount.getMoney()-money);
            toAccount.setMoney(toAccount.getMoney()+money);

            //完成转账操作
            ad.updateAccout(fromAccount);
//            int i = 10/0;
            ad.updateAccout(toAccount);

            ManagerThreadLocal.commit();//提交事务
        } catch (Exception e) {
            try {
                ManagerThreadLocal.rollback();//回滚事务
            } catch (Exception e1) {
                e1.printStackTrace();
            }
        }finally{
            try {
                ManagerThreadLocal.close();
            } catch (Exception e) {
                e.printStackTrace();
            }//关闭
        }
    }

}

4.创建ManagerThreadLocal管理Connection

package com.learning.util;

import java.sql.Connection;
import java.sql.SQLException;

public class ManagerThreadLocal {
    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    //得到一个连接
    public static Connection getConnection(){
        Connection conn = tl.get();//从当前线程中取出一个连接
        if(conn==null){
            conn = C3P0Util.getConnection();//从池中取出一个
            tl.set(conn);//把conn对象放入到当前线程对象中
        }
        return conn;
    }

    //开始事务
    public static void startTransacation(){
        try {
            Connection conn = getConnection();
            conn.setAutoCommit(false);//从当前线程对象中取出的连接，并开始事务
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static void commit(){
        try {
            getConnection().commit();//提交事务
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static void rollback(){
        try {
            getConnection().rollback();//回滚事务
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static void close(){
        try {
            getConnection().close();//把连接放回池中
            tl.remove();//把当前线程对象中的conn移除
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}