数据库表的设计和准备数据

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环境搭建

在pom.xml中配置依赖（logback、mybatis、mysql、servlet）
注意引入tomcat

前端页面编写

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>银行账户转账</title>
</head>
<body>
    <form action="/bank/transfer" method="post">
        转出账户：<input type="text" name="fromActno"><br>
        转入账号：<input type="text" name="toActno"><br>
        转账金额：<input type="text" name="money"><br>
        <input type="submit" value="转账">
    </form>
</body>
</html>

后端代码实现

后端代码目录

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dao层

//AccountDaoImpl
package com.example.bank.dao.impl;

import com.example.bank.dao.AccountDao;
import com.example.bank.pojo.Account;
import com.example.bank.utils.SqlSessionUtil;
import org.apache.ibatis.session.SqlSession;

public class AccountDaoImpl implements AccountDao {
    @Override
    public Account selectByActno(String actno) {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        Account account = (Account) sqlSession.selectOne("account.selectByActno", actno);
        sqlSession.close();
        return account;
    }

    @Override
    public int updateByActno(Account act) {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        int count = sqlSession.update("account.updateByActno",act);
        sqlSession.commit();
        sqlSession.close();
        return count;
    }
}

package com.example.bank.dao;

import com.example.bank.pojo.Account;

//dao对象中的任何一个方法和业务不挂钩，没有任何业务逻辑在里面
//DAO中的方法就是做CRUD的
public interface AccountDao {
    //根据账号查询账户信息
    Account selectByActno(String actno);
    //更新账户信息
    int updateByActno(Account act);
}

dao层是三层架构的最底层，是数据访问层，主要是连接MySQL，并做数据的CRUD，不包含任何的逻辑

service

//AccountServiceImpl
package com.example.bank.service.impl;

import com.example.bank.dao.AccountDao;
import com.example.bank.dao.impl.AccountDaoImpl;
import com.example.bank.exceptions.MoneyNotEnoughException;
import com.example.bank.exceptions.TransferException;
import com.example.bank.pojo.Account;
import com.example.bank.service.AccountService;

public class AccountServiceImpl implements AccountService {
    private AccountDao accountDao = new AccountDaoImpl();
    @Override
    public void transfer(String fromActno, String toActno, double money) throws MoneyNotEnoughException, TransferException {
        //1、判断转出账户的余额是否充足
        Account fromAct = accountDao.selectByActno(fromActno);
        if (fromAct.getBalance() < money){
            //2、如果转出账户余额不足，提示用户
            throw new MoneyNotEnoughException("对不起，您的余额不足");
        }
        //3、如果转出账户余额充足，更新转出账户余额（update）
        //先更新内存中java对象account的余额
        Account toAct = accountDao.selectByActno(toActno);
        fromAct.setBalance(fromAct.getBalance() - money);
        toAct.setBalance(toAct.getBalance() + money);
        int count = accountDao.updateByActno(fromAct);
        //4、更新转入账户余额（update）
        count += accountDao.updateByActno(toAct);
        if (count != 2){
            throw new TransferException("转账异常，未知原因");
        }
    }

}

//AccountService
package com.example.bank.service;

import com.example.bank.exceptions.MoneyNotEnoughException;
import com.example.bank.exceptions.TransferException;

public interface AccountService {
//    @param fromActno 转出账号
//    @param toActno 转入账号
//    @param money 转账金额
    void transfer(String fromActno, String toActno, double money) throws MoneyNotEnoughException, TransferException;
}

service层是业务逻辑层，主要是对数据进行逻辑的处理，页面的改变等。这里的逻辑主要就是对余额先进行能否转移的判断，其次是对账户余额的转移改变，最后就是对不同错误的出现返回不同的错误类型

web

//AccountServlet
package com.example.bank.web;

import com.example.bank.exceptions.MoneyNotEnoughException;
import com.example.bank.exceptions.TransferException;
import com.example.bank.service.AccountService;
import com.example.bank.service.impl.AccountServiceImpl;


import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/transfer")
public class AccountServlet extends HttpServlet {
    //为了让这个对象在其他方法中也可以用
    private AccountService accountService = new AccountServiceImpl();
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws IOException{
        //获取表单数据
        String fromActno = request.getParameter("fromActno");
        String toActno = request.getParameter("toActno");
        double money = Double.parseDouble(request.getParameter("money"));

        try {
            //调用servlet的转账方法完成转账。（调业务层）
            accountService.transfer(fromActno,toActno,money);
            //程序能够走到这里，表示转账一定成功了
            //调用view完成展示结果
            response.sendRedirect(request.getContextPath() + "/success.html");
        } catch (MoneyNotEnoughException e) {
            response.sendRedirect(request.getContextPath() + "/error1.html");
        } catch (TransferException e) {
            response.sendRedirect(request.getContextPath() + "/error2.html");
        }
    }
}

展示层，获取表单数据以及针对不同情况错误的出现展示不同的页面信息。

pojo

pojo是封装类，账号的类型里面有的相关数据，一方面能在java中进行数据操作，另一方面对接MySQL的账户信息，方便CRUD。

package com.example.bank.web;

import com.example.bank.exceptions.MoneyNotEnoughException;
import com.example.bank.exceptions.TransferException;
import com.example.bank.service.AccountService;
import com.example.bank.service.impl.AccountServiceImpl;


import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/transfer")
public class AccountServlet extends HttpServlet {
    //为了让这个对象在其他方法中也可以用
    private AccountService accountService = new AccountServiceImpl();
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws IOException{
        //获取表单数据
        String fromActno = request.getParameter("fromActno");
        String toActno = request.getParameter("toActno");
        double money = Double.parseDouble(request.getParameter("money"));

        try {
            //调用servlet的转账方法完成转账。（调业务层）
            accountService.transfer(fromActno,toActno,money);
            //程序能够走到这里，表示转账一定成功了
            //调用view完成展示结果
            response.sendRedirect(request.getContextPath() + "/success.html");
        } catch (MoneyNotEnoughException e) {
            response.sendRedirect(request.getContextPath() + "/error1.html");
        } catch (TransferException e) {
            response.sendRedirect(request.getContextPath() + "/error2.html");
        }
    }
}

Utils

package com.example.bank.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;

public class SqlSessionUtil {
    private SqlSessionUtil(){}

    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    public static SqlSession openSession(){
        return sqlSessionFactory.openSession();
    }

}