在web中应用mybatis

搭建环境

数据库表的设计

create table bank(id bigint auto_increment primary key ,actno varchar(255) comment "账号",balance decimal(15,2) comment "余额"
);
insert into bank values(1,'act001',50000);
insert into bank values(2,'act002',0);

添加依赖

 <!--mybatis依赖--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.10</version></dependency><!--mysql驱动依赖--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.30</version></dependency><!--junit依赖--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope></dependency><!--logback依赖--><dependency><groupId>ch.qos.logback</groupId><artifactId>logback-classic</artifactId><version>1.2.11</version></dependency><!--servlet依赖--><dependency><groupId>jakarta.servlet</groupId><artifactId>jakarta.servlet-api</artifactId><version>5.0.0</version><scope>provided</scope></dependency><build><finalName>mybatis-004-web</finalName><pluginManagement><plugins><plugin><artifactId>maven-clean-plugin</artifactId><version>3.1.0</version></plugin><plugin><artifactId>maven-resources-plugin</artifactId><version>3.0.2</version></plugin><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.8.0</version></plugin><plugin><artifactId>maven-surefire-plugin</artifactId><version>2.22.1</version></plugin><plugin><artifactId>maven-war-plugin</artifactId><version>3.2.2</version></plugin><plugin><artifactId>maven-install-plugin</artifactId><version>2.5.2</version></plugin><plugin><artifactId>maven-deploy-plugin</artifactId><version>2.8.2</version></plugin></plugins></pluginManagement></build>

引入配置文件

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/xun
jdbc.username=root
jdbc.password=root

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><properties resource="jdbc.properties"/><environments default="dev"><environment id="dev"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="url" value="${jdbc.url}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment></environments><mappers><!--一定要注意这里的路径哦！！！--><mapper resource="AccountMapper.xml"/></mappers>
</configuration>

<?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="account"></mapper>

前端页面

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>银行账户转账</title>
</head>
<body>
<!--/bank是应用的根，部署web应用到tomcat的时候一定要注意这个名字-->
<form action="/bank/transfer" method="post">转出账户：<input type="text" name="fromActno"/><br>转入账户：<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>

业务代码编写

定义pojo类

package com.xun.bank.pojo;public class Account {private Long id;private String actno;private Double balance;@Overridepublic String toString() {return "Account{" +"id=" + id +", actno='" + actno + '\'' +", balance=" + balance +'}';}public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getActno() {return actno;}public void setActno(String actno) {this.actno = actno;}public Double getBalance() {return balance;}public void setBalance(Double balance) {this.balance = balance;}public Account(Long id, String actno, Double balance) {this.id = id;this.actno = actno;this.balance = balance;}public Account() {}
}

编写AccountDao接口，以及AccountDaoImpl实现类

dao类

是负责对数据进行操作的类，只负责数据的增删改查，不牵扯到任何业务

分析dao中至少要提供几个方法，才能完成转账：

转账前需要查询余额是否充足：selectByActno
转账时要更新账户：update

package com.xun.bank.dao;import com.xun.bank.pojo.Account;public interface AccountDao {//根据账号获取用户信息Account selectByActno(String actno);//更新账户信息int update(Account act);
}

package com.xun.bank.daoimpl;import com.xun.bank.dao.AccountDao;
import com.xun.bank.pojo.Account;
import com.xun.bank.utils.SqlSessionUtil;
import org.apache.ibatis.session.SqlSession;public class AccountDaoImpl implements AccountDao {@Overridepublic Account selectByActno(String actno) {SqlSession sqlSession = SqlSessionUtil.openSession();Account act =(Account) sqlSession.selectOne("selectByActno",actno);//进行类型强转sqlSession.close();return act;}@Overridepublic int update(Account act) {SqlSession sqlSession = SqlSessionUtil.openSession();int count = sqlSession.update("update", act);sqlSession.commit();sqlSession.close();return count;}
}

写了dao类，就需要用到SQL映射文件了

<?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="account"><select id="selectByActno" resultType="com.xun.bank.pojo.Account">select id,actno,balance from bank where actno = #{actno};</select><update id="update">update bank set balance = #{balance} where actno =#{actno};</update></mapper>

编写AccountService接口以及AccountServiceImpl

service类专注于处理业务

package com.xun.bank.service;import com.xun.bank.exception.AppException;
import com.xun.bank.exception.MoneyNotEnoughException;public interface AccountService {void transfer(String fromActno, String toActno, double money) throws MoneyNotEnoughException, AppException;
}

package com.xun.bank.serviceimpl;import com.xun.bank.dao.AccountDao;
import com.xun.bank.daoimpl.AccountDaoImpl;
import com.xun.bank.exception.AppException;
import com.xun.bank.exception.MoneyNotEnoughException;
import com.xun.bank.pojo.Account;
import com.xun.bank.service.AccountService;public class AccountServiceImpl implements AccountService {AccountDao accountDao = new AccountDaoImpl();@Overridepublic void transfer(String fromActno, String toActno, double money) throws MoneyNotEnoughException, AppException {//查出转出账户余额Account fromact = accountDao.selectByActno(fromActno);if(fromact.getBalance() < money){throw new MoneyNotEnoughException("对不起，账户余额不足");}try{Account toact = accountDao.selectByActno(toActno);fromact.setBalance(fromact.getBalance() - money);toact.setBalance(toact.getBalance() + money);accountDao.update(fromact);accountDao.update(toact);}catch(Exception e){throw new AppException("转账失败，未知原因");}}
}

编写异常类

package com.xun.bank.exception;public class MoneyNotEnoughException extends Exception{public MoneyNotEnoughException(){}public MoneyNotEnoughException(String msg){ super(msg); }
}

package com.xun.bank.exception;public class AppException extends Exception{public AppException(){}public AppException(String msg){ super(msg); }
}

编写AccountController

controller类是控制器，接受前端的请求，调用相关的service完成业务

package com.xun.bank.controller;import com.xun.bank.exception.AppException;
import com.xun.bank.exception.MoneyNotEnoughException;
import com.xun.bank.service.AccountService;
import com.xun.bank.serviceimpl.AccountServiceImpl;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;import java.io.IOException;
import java.io.PrintWriter;
@WebServlet("/transfer")
public class AccountController extends HttpServlet {private AccountService accountService= new AccountServiceImpl();@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取响应流response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();String fromActno = request.getParameter("fromActno");String toActno = request.getParameter("toActno");double money = Integer.parseInt(request.getParameter("money"));try{accountService.transfer(fromActno,toActno,money);out.println("<h1>转账成功！！！</h1>");}catch (MoneyNotEnoughException e){out.println(e.getMessage());}catch (AppException e){out.println(e.getMessage());}}
}