一、转账功能需求分析

           转账简易页面

转账方需提供帐号及其密码，输入相应的金额，还需提供收款方的账号及其姓名。

二、数据库设计

根据以上的简单需求可分析出，只需要一张表（Account）就可以解决问题，其中包含帐号、密码、账户余额和姓名。

示例数据：

三、程序编写

       按照MVC开发模式的项目开发一般顺序进行编写。

       首先新建一个Web项目

• 3.1 实体类Account

         其中的密码当时写的是int型，可修改成String类型。

package com.ccnu.pojo;public class Account {private int id;private String accNo;private int password;private String name;private double balance;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getAccNo() {return accNo;}public void setAccNo(String accNo) {this.accNo = accNo;}public int getPassword() {return password;}public void setPassword(int password) {this.password = password;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getBalance() {return balance;}public void setBalance(double balance) {this.balance = balance;}}

•  3.2 数据访问层（持久层）

          该示例使用MyBatis框架实现数据访问层的开发

         3.2.1 mybatis全局配置文件

         在src文件夹下新建xml文件mybatis.xml，文件名可以随意取。

          该配置文件中的配置标签有顺序，若不按照顺序进行配置，则会报错。

  其中的<typeAliases>标签，为配置别名标签，标签<package>为直接给包下所有的类取别名，别名为类名，不区分大小写。

     3.2.2 mapper文件

           新建包，在包下新建xml文件，取名叫做AccountMapper.xml

      mapper文件中写sql查询语句。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.ccnu.mapper.AccountMapper"><!-- 根据帐号和密码查询账户信息 --><select id="selByAccnoPwd" resultType="account" parameterType="account">select * from account where accno=#{accNo} and password=#{password}</select><!-- 根据账号和姓名查询账户信息 --><select id="selByAccnoName" resultType="account" parameterType="account">select * from account where accno=#{accNo} and name=#{name}</select><!-- 根据accNo修改账户余额 --><update id="updBalanceByAccno" parameterType="account">update account set balance=balance+#{balance} where accno=#{accNo}</update>
</mapper>

• 3.3 业务逻辑层（service）

           3.3.1 新建接口类AccountService.java

              前面为要返回给客户端的状态码，transfer方法有两个参数，两个对象参数，一个转出账户，一个转进账户。

public interface AccountService {/*** 帐号和密码不匹配的状态码*/int ACCOUNT_PASSWORD_NOT_MATCH = 1;/*** 余额不足*/int ACCOUNT_BALANCE_NOT_ENOUGH = 2;/*** 帐号和姓名不匹配状态码*/int ACCOUNT_NAME_NOT_MATCH = 3;/*** 转账失败*/int ERROR = 4;/*** 转账成功*/int SUCCESS = 5;/*** 转账* * @param accIn*            收款帐号* @param accOut*            转出帐号* @return*/int transfer(Account accIn, Account accOut) throws IOException;}

        3.3.2 实现类AccountServiceImpl.java

              对数据库进行增删改要提交事务，session.commit()。

package com.ccnu.service.impl;import java.io.IOException;
import java.io.InputStream;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 com.ccnu.pojo.Account;
import com.ccnu.service.AccountService;public class AccountServiceImpl implements AccountService {@Overridepublic int transfer(Account accIn, Account accOut) throws IOException {InputStream is = Resources.getResourceAsStream("mybatis.xml");SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);SqlSession session = factory.openSession();// 先判断帐号和密码是否匹配Account accOutselect = session.selectOne("com.ccnu.mapper.AccountMapper.selByAccnoPwd", accOut);if (accOutselect != null) {if (accOutselect.getBalance() >= accOut.getBalance()) {// 判断收款帐号和姓名是否匹配Account accInselect = session.selectOne("com.ccnu.mapper.AccountMapper.selByAccnoName", accIn);if (accInselect != null) {// 可以转账accIn.setBalance(accOut.getBalance());accOut.setBalance(-accOut.getBalance());int index = session.update("com.ccnu.mapper.AccountMapper.updBalanceByAccno", accOut);index += session.update("com.ccnu.mapper.AccountMapper.updBalanceByAccno", accIn);if (index == 2) {// 转账成功session.commit();session.close();return SUCCESS;} else {// 转账失败session.rollback();session.close();return ERROR;}} else {// 收款帐号和姓名不匹配return ACCOUNT_NAME_NOT_MATCH;}} else {// 余额不足return ACCOUNT_BALANCE_NOT_ENOUGH;}} else {// 帐号和密码不匹配return ACCOUNT_PASSWORD_NOT_MATCH;}}}

• 3.4 Servlet

package com.ccnu.servlet;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import com.ccnu.pojo.Account;
import com.ccnu.service.AccountService;
import com.ccnu.service.impl.AccountServiceImpl;@WebServlet("/transfer")
public class TransferServlet extends HttpServlet {private AccountService accountService = new AccountServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {// 当请求方传入的数据中包含中文字符时，要设置字符编码req.setCharacterEncoding("utf-8");Account accOut = new Account();accOut.setAccNo(req.getParameter("accOutAccNo"));accOut.setPassword(Integer.parseInt(req.getParameter("accOutPassword")));accOut.setBalance(Double.parseDouble(req.getParameter("accOutBalance")));Account accIn = new Account();accIn.setAccNo(req.getParameter("accInAccNo"));accIn.setName(req.getParameter("accInName"));int index = accountService.transfer(accIn, accOut);if (index == AccountService.SUCCESS) {// 转账成功res.sendRedirect("/bank/log.jsp");} else {// 转账失败HttpSession session = req.getSession();session.setAttribute("code", index);res.sendRedirect("/bank/error/error.jsp");}}
}

• 3.5 编写相应的视图

             index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="transfer" method="post">转账帐号：<input type="text" name="accOutAccNo"><br>密码：<input type="password" name="accOutPassword"><br>金额：<input type="text" name="accOutBalance"><br>收款帐号：<input type="text" name="accInAccNo"><br>收款姓名：<input type="text" name="accInName"><br><input type="submit" value="转账">
</form>
</body>
</html>