转账案例

四.转账案例:
描述:一个人的账户减少,另一个人的账户增加相同金额.
步骤:
     1.Eclipse创建工程transfer,并添加jar包:mysql-connector;c3p0(c3p0-config.xml放在src文件夹下);commens-dbutils;
     2.创建5个包:web/service/DAO/Account类/utils
     3.创建数据库bank,添加数据表account(id,name,money);(用于与Account类相关联)
     4.web层是供客户使用的,只用于输入信息,及展示运行结果(转账成功或失败)
     5.serive层用于转账操作,并返回给web层转账成功或失败的信息;
     6.DAO层用于操作数据库,即查询是否有客户输入的相关信息,并将查询结果封装成类(javabean),返回给service层;
代码演示:
web层:
    

package huguangqin.cnblogs.web;
     import huguangqin.cnblogs.service.Service;
     import java.util.Scanner;
     //该层展示给客户,用于收集信息,展示数据及结果
    public class MyAPP {
         public static void main(String[] args) {
             // 提示用户输入
            Scanner sc = new Scanner(System.in);
             System.out.print("请输入付款人姓名:");
             String payName = sc.next();
             System.out.print("请输入收款人姓名:");
             String receiptName = sc.next();
             System.out.print("请输入金额:");
             double money = sc.nextDouble();

             // 面向service层,返回转账结果
            Service ser = new Service();
            String message = ser.transfer(payName, receiptName, money);
             System.out.println(message);
         }

    }

service层:
    

package huguangqin.cnblogs.service;
     import huguangqin.cnblogs.DAO.DAO;
     import huguangqin.cnblogs.domain.Account;
     import huguangqin.cnblogs.utils.ConnectionManager;
     public class Service {
         public String transfer(String payName, String receiptName, double money) {
             // 开启事务
            ConnectionManager.startTransaction();

             // 根据传入的收/付款人姓名在数据库中查找是否存在--以后所有的步骤都是面向Account操作
            DAO d = new DAO();
             Account payAccount = d.queryAccount(payName);
             if (payAccount == null) {
                 ConnectionManager.rollback();
                 return "付款账户不存在";
             }

             Account receiptAccount = d.queryAccount(receiptName);
             if (receiptAccount == null) {
                 ConnectionManager.rollback();
                 return "收款账户不存在";
             }

             // 根据传入的金额,查询余额是否足够
            if (payAccount.getMoney() >= money) {
                 payAccount.setMoney(payAccount.getMoney() - money);
             } else {
                 ConnectionManager.rollback();
                 return "余额不足";
             }
             receiptAccount.setMoney(receiptAccount.getMoney() + money);

             int i = d.update(payAccount);
             int j = d.update(receiptAccount);

             // 根据操作的结果,返回操作是否成功
            if (i == 1 && j == 1) {
                 ConnectionManager.commit();
                 return "转账成功,金额:" + money + "元";
             } else {
                 ConnectionManager.rollback();
                 return "服务器升级...,转账失败";
             }
         }
     }

DAO(Data Access Object)层:
    

package huguangqin.cnblogs.DAO;
     import huguangqin.cnblogs.domain.Account;
     import huguangqin.cnblogs.utils.ConnectionManager;
     import java.sql.Connection;
     import java.sql.SQLException;
     import org.apache.commons.dbutils.QueryRunner;
     import org.apache.commons.dbutils.handlers.BeanHandler;
     //该层用于操作数据库-创建-查询-更新
    public class DAO {
         // 能否将QueryRunner/Connection作为成员变量?
         private static QueryRunner qr = new QueryRunner();
         private static Connection conn = ConnectionManager.getConnectionThreadLocal();

         /*
          * 查询数据库 返回值:Account 参数:String name 方法名:queryAccount
          */
         public Account queryAccount(String name) {
             // 获取本地线程连接对象
            String querySql = "SELECT * FROM account WHERE name = ?";
             BeanHandler<Account> bh = new BeanHandler<>(Account.class);
             Account queryAccount = null;
             try {
                 queryAccount = qr.query(conn, querySql, bh, name);
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             return queryAccount;
         }

         /*
          * 更新数据库 方法名:update 返回值:int 参数:money-转账金额
         */

         public int update(Account a) {
             String updateSql = "UPDATE account SET money = ? WHERE id = ?";
             int i = 0;
             try {
                 i = qr.update(conn, updateSql, a.getMoney(), a.getId());
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             return i;
         }
     }

domain层:
    

package huguangqin.cnblogs.domain;
     //javabean
     public class Account {
         private int id;// 账户ID
         private String name;// 账户名
        private double money;// 余额

         public Account() {
             super();
         }

         public Account(int id, String name, double money) {
             super();
             this.id = id;
             this.name = name;
             this.money = money;
         }

         public int getId() {
             return id;
         }

         public void setId(int id) {
             this.id = id;
         }

         public String getName() {
             return name;
         }

         public void setName(String name) {
             this.name = name;
         }

         public double getMoney() {
             return money;
         }

         public void setMoney(double money) {
             this.money = money;
         }

         @Override
         public String toString() {
            return "Account [id=" + id + ", name=" + name + ", money=" + money
                     + "]";
         }

     }

utils包://ConnectionManager工具
    

package huguangqin.cnblogs.utils;
     import java.sql.Connection;
     import java.sql.SQLException;
     //该工具用于事务管理
    public class ConnectionManager {
         // 面向Connection进行事务管理,因此首先获取Connection,并存放于ThreadLocal,规避线程安全问题
        private static ThreadLocal<Connection> threadLocal = new ThreadLocal<>();

         // 获取本线程的Connection连接,因为后面的事务管理全部是面向Connection对象的
        public static Connection getConnectionThreadLocal() {
             Connection conn = threadLocal.get();// 注意要从当前线程获取,不要利用MyC3P0创建!!!
             if (conn == null) {
                 // 如果连接为空,则通过MyC3P0工具获取并存放线程一个连接
                conn = MyC3P0.getConnection();
                 threadLocal.set(conn);
             }
             return conn;
         }

         // 面向获取到的本地线程的连接对象,开启事务
        public static void startTransaction() {
             try {
                 getConnectionThreadLocal().setAutoCommit(false);
             } catch (SQLException e) {
                 e.printStackTrace();
                 throw new RuntimeException("事务开启失败");
             }
         }

         // 面向本地线程的连接对象,提交事务
        public static void commit() {
             try {
                 getConnectionThreadLocal().commit();
             } catch (SQLException e) {
                 e.printStackTrace();
                 throw new RuntimeException("提交失败!");
             }
         }

         // 面向本地线程的连接对象,回滚事务
        public static void rollback() {
             try {
                 getConnectionThreadLocal().rollback();
             } catch (SQLException e) {
                 e.printStackTrace();
                 throw new RuntimeException("回滚失败!");
             }
        }
     }

//MyC3P0工具类
   

 package huguangqin.cnblogs.utils;
     import java.sql.Connection;
     import java.sql.SQLException;
     import javax.sql.DataSource;
     import com.mchange.v2.c3p0.ComboPooledDataSource;

     //MyC3P0工具用于建立资源池,并从池中获取Connection
     public class MyC3P0 {
         // 创建连接池
        private static DataSource ds = new ComboPooledDataSource();

         // 创建方法获取资源池中Connection对象
        public static Connection getConnection() {
             Connection conn = null;
             try {
                 conn = ds.getConnection();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             return conn;
         }

         // 返回连接池
        public static DataSource getDataSource() {
             return ds;
         }

     }