12345103000（4） 工具类 ： JdbcUtils
package com.itheima.transfer.utils;?import com.mchange.v2.c3p0.ComboPooledDataSource;import java.sql.Connection;import java.sql.SQLException;?public class JdbcUtils {// c3p0 数据库连接池对象属性private static final ComboPooledDataSource ds = new ComboPooledDataSource();// 获取连接public static Connection getConnection() throws SQLException {return ds.getConnection();}//释放资源public static void release(AutoCloseable... ios){for (AutoCloseable io : ios) {if(io != null){try {io.close();} catch (Exception e) {e.printStackTrace();}}}}public static void commitAndClose(Connection conn) {try {if(conn != null){//提交事务conn.commit();//释放连接conn.close();}} catch (SQLException e) {e.printStackTrace();}}?public static void rollbackAndClose(Connection conn) {try {if(conn != null){//回滚事务conn.rollback();//释放连接conn.close();}} catch (SQLException e) {e.printStackTrace();}}}（5） dao层代码 ： AccountDao
package com.itheima.transfer.dao;?import com.itheima.transfer.utils.JdbcUtils;?import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;?public class AccountDao {?public void out(String outUser, int money) throws SQLException {String sql = "update account set money = money - ? where name = ?";?Connection conn = JdbcUtils.getConnection();PreparedStatement pstm = conn.prepareStatement(sql);pstm.setInt(1,money);pstm.setString(2,outUser);pstm.executeUpdate();?JdbcUtils.release(pstm,conn);}?public void in(String inUser, int money) throws SQLException {String sql = "update account set money = money + ? where name = ?";?Connection conn = JdbcUtils.getConnection();PreparedStatement pstm = conn.prepareStatement(sql);pstm.setInt(1,money);pstm.setString(2,inUser);pstm.executeUpdate();?JdbcUtils.release(pstm,conn);}}（6） service层代码 ： AccountService
package com.itheima.transfer.service;?import com.itheima.transfer.dao.AccountDao;import java.sql.SQLException;?public class AccountService {?public boolean transfer(String outUser, String inUser, int money) {AccountDao ad = new AccountDao();try {// 转出ad.out(outUser, money);// 转入ad.in(inUser, money);} catch (Exception e) {e.printStackTrace();return false;}return true;}}（7） web层代码 ： AccountWeb
package com.itheima.transfer.web;import com.itheima.transfer.service.AccountService;public class AccountWeb {public static void main(String[] args) {// 模拟数据 : Jack 给 Rose 转账 100String outUser = "Jack";String inUser = "Rose";int money = 100;AccountService as = new AccountService();boolean result = as.transfer(outUser, inUser, money);if (result == false) {System.out.println("转账失败!");} else {System.out.println("转账成功!");}}}2.1.2 引入事务案例中的转账涉及两个DML操作： 一个转出 ， 一个转入 。 这些操作是需要具备原子性的 ， 不可分割 。 不然就有可能出现数据修改异常情况 。
public class AccountService {public boolean transfer(String outUser, String inUser, int money) {AccountDao ad = new AccountDao();try {// 转出ad.out(outUser, money);// 模拟转账过程中的异常int i = 1/0;// 转入ad.in(inUser, money);} catch (Exception e) {e.printStackTrace();return false;}return true;}}