MVC模式分层练习-编程知识

新建库

新建表

插入点数据

先不用MVC模式写功能,来看下缺点是什么

新建一个空项目

选项项目使用的JDK

自己的IDEA总是要重启下

新建模块

因maven还没教

添加框架支持

添加后项目多了这些

添加些必要依赖这里注意下,如果导入jar包不对可以重新导入下或者是jar包本身出了问题

添加页面

配置Tomcat

启动

请求地址因现在没有后端

现在写后端并测试

解决控制台输出乱码问题

System.out输出乱码

需要用到JDBC连接Mysql数据库

导入Mysql驱动jar包

java web项目一般会在WEB-INF下有个lib用来放Tomcat内没有,外部引入的依赖

可以创建个lib目录然后将jar包复制进来

具体代码

package com.bank.web;import com.bank.exception.AppException;
import com.bank.exception.MoneyNotEnoughException;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 java.io.*;
import java.sql.*;
import java.util.Locale;/*** 在不使用MVC架构模式的前提下,完成银行账户转账* 分析这个程序存在哪些问题?* @author hrui* @date 2023/8/31 23:06*/
@WebServlet("/transfer")
public class AccountTransferServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取响应流对象resp.setContentType("text/html;charset=UTF-8");PrintWriter writer = resp.getWriter();//获取前端传来的参数String fromActno = req.getParameter("fromActno");String toActno = req.getParameter("toActno");double money = Double.parseDouble(req.getParameter("money"));
//        System.out.println("转出账户:"+fromActno);
//        System.out.println("转入账户:"+fromActno);
//        System.out.println("转账金额:"+fromActno);//编写转账的业务逻辑代码,连接数据库,进行转账操作//1.转账之前要判断转出账户的余额是否充足Connection conn=null;PreparedStatement ps=null;//PreparedStatement ps2=null;ResultSet rs=null;try {//注册驱动Class.forName("com.mysql.cj.jdbc.Driver");//获取连接conn = DriverManager.getConnection("xxx", "xxx", "xxx");conn.setAutoCommit(false);//获取执行对象String sql="select balance from t_act where actno=?";ps = conn.prepareStatement(sql);ps.setString(1, fromActno);//执行sql,返回结果集rs = ps.executeQuery();//获取结果集if(rs.next()){double balance = rs.getDouble("balance");if(balance<money){//余额不足(使用异常处理机制)throw new MoneyNotEnoughException("余额不足");}//程序能到这里,说明余额重组  不需要else//开始转账sql="update t_act set balance=balance-? where actno=?";ps = conn.prepareStatement(sql);ps.setDouble(1, money);ps.setString(2, fromActno);int count = ps.executeUpdate();//模拟异常String str=null;str.toString();sql="update t_act set balance=balance+? where actno=?";ps=conn.prepareStatement(sql);ps.setDouble(1, money);ps.setString(2, toActno);//累计count += ps.executeUpdate();if(count!=2){throw new AppException("app异常,请联系管理员");}}conn.commit();writer.print("转账成功");} catch (ClassNotFoundException | SQLException | MoneyNotEnoughException | AppException e) {try {if(conn!=null) {conn.rollback();}} catch (SQLException e1) {e1.printStackTrace();}e.printStackTrace();writer.print(e.getMessage());}finally {//释放资源,根据JDBC规范 从小到大if(rs!=null){try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if(ps!=null){try {ps.close();} catch (SQLException e) {e.printStackTrace();}}if(conn!=null){try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}}
}

1>负责了数据接收

2>负责了核心业务处理

3>负责了数据库表中的CRUD操作(Create(增) Retrieve(查) Update(改) Delete(删))

4>负责了数据的页面展示

引起的缺点:

代码复用性差比如查余额,可以抽取出来,单独放到一个方法

代码复用性差的原因,没有职能分工,独立组件的概念,代码之间耦合度高,扩展力差

操作数据库代码和业务逻辑混杂在一起,容易出错,无法专注于业务逻辑书写

下面以MVC的模式对上面代码改进

1.系统为什么要分层?

希望专人干专事.各司其职.分工明确.这样可以降低耦合,扩展增强.复用增强

2.软件架构中,有一个非常著名的架构模式:MVC模式

M(Model:数据/业务) V(View:视图/展示) C(Controller:控制器/核心)

首先是对JDBC的封装

JDBC工具类

package com.bank.utils;import java.sql.*;
import java.util.ResourceBundle;/*** @author hrui* @date 2023/9/1 10:24*/
public class DBUtil {private static ResourceBundle bundle=ResourceBundle.getBundle("resources/jdbc");private static String driver=bundle.getString("driver");private static String url=bundle.getString("url");private static String username=bundle.getString("username");private static String password=bundle.getString("password");//不让创建对象,原因工具类方法一般都静态的,无需外部创建对象//为防止外部创建对象,构造私有化private DBUtil(){}//DBUtil类加载时注册驱动static{try {Class.forName(driver);} catch (ClassNotFoundException e) {e.printStackTrace();}}//没有使用连接池,直接创建的连接对象public static Connection getConnection() throws SQLException {Connection conn= DriverManager.getConnection(url,username,password);return conn;}public static void close(Connection conn, Statement statement, ResultSet rs){if(rs!=null){try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if(statement!=null){try {statement.close();} catch (SQLException e) {e.printStackTrace();}}if(conn!=null){try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}
}

测试连接

封装实体类

package com.bank.mvc;import java.util.Objects;/*** 账户实体类,用于封装账户信息* POJO对象* 有的人也会把这种专门封装数据的对象,称为bean对象(javabean:咖啡豆)* 有的人也会把这种专门分装数据的对象,称为领域模型对象.domain对象.* pojo,bean,domain* @author hrui* @date 2023/9/1 15:34*/
public class Account {private Long id;private String actno;private Double balance;public Account() {}public Account(Long id, String actno, Double balance) {this.id = id;this.actno = actno;this.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;}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Account acount = (Account) o;return id.equals(acount.id) && actno.equals(acount.actno) && balance.equals(acount.balance);}@Overridepublic int hashCode() {return Objects.hash(id, actno, balance);}@Overridepublic String toString() {return "Account{" +"id=" + id +", actno='" + actno + '\'' +", balance=" + balance +'}';}
}

编写DAO层

package com.bank.mvc;import com.bank.utils.DBUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;/*** 负责Acount数据的增删改查* 1.什么是DAO*      Data Access Object(数据访问对象)* 2.DAO实际上是一种设计模式,属于JAVAEE的设计模式之一.(不是23种设计模式)* 3.DAO只负责数据库CRUD,没有任何业务逻辑* 4.没有任何业务逻辑,只负责表中数据增删改查,有一个特殊的称谓:DAO对象* @author hrui* @date 2023/9/1 12:39*/
public class AccountDao {public int insert(Account act){Connection conn=null;PreparedStatement ps=null;int count=0;try {conn= DBUtil.getConnection();String sql="insert into t_act(actno,balance) values (?,?)";ps=conn.prepareStatement(sql);ps.setString(1, act.getActno());ps.setDouble(2, act.getBalance());count=ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(conn,ps,null);}return count;}public int deleteByActno(Long id){Connection conn=null;PreparedStatement ps=null;int count=0;try {conn=DBUtil.getConnection();String sql="delete from t_act where id=?";ps=conn.prepareStatement(sql);ps.setLong(1, id);count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(conn,ps,null);}return count;}public int update(Account act){Connection conn=null;PreparedStatement ps=null;int count=0;try {conn=DBUtil.getConnection();String sql="update t_act set balance=? where id=?";ps=conn.prepareStatement(sql);ps.setDouble(1, act.getBalance());ps.setLong(2, act.getId());count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(conn,ps,null);}return count;}public Account selectBtActNo(String actno){Connection conn=null;PreparedStatement ps=null;ResultSet rs=null;Account account=new Account();try {conn=DBUtil.getConnection();String sql="select id,actno,balance from t_act where actno=?";ps=conn.prepareStatement(sql);ps.setString(1, actno);rs = ps.executeQuery();if(rs.next()){Long id=rs.getLong("id");String actno1=rs.getString("actno");Double balance=rs.getDouble("balance");account.setId(id);account.setActno(actno1);account.setBalance(balance);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(conn,ps,null);}return account;}public List<Account> selectAll(){Connection conn=null;PreparedStatement ps=null;ResultSet rs=null;List<Account> list=new ArrayList<>();try {conn=DBUtil.getConnection();String sql="select id,actno,balance from t_act ";ps=conn.prepareStatement(sql);rs = ps.executeQuery();while(rs.next()){Long id=rs.getLong("id");String actno=rs.getString("actno");Double balance=rs.getDouble("balance");Account account=new Account();account.setId(id);account.setActno(actno);account.setBalance(balance);list.add(account);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(conn,ps,null);}return list;}
}

原先在Servlet里

1>负责了数据接收

2>负责了狠心业务处理

3>负责了数据库表中数据CRUD操作

4>负责了页面数据展示

现在已经一层层分离了

两个异常类

用AccountSAervice来做业务处理

具体业务处理代码

package com.bank.mvc;import com.bank.exception.AppException;
import com.bank.exception.MoneyNotEnoughException;/*** Service:业务* 专门处理Account的业务处理类* 该类只专注业务处理* 主要专注于MVC模式,不需要专注于取什么名字  xxx都可以* @author hrui* @date 2023/9/2 0:49*/
public class AccountService {private AccountDao accountDao=new AccountDao();/*** 完成转账的业务逻辑* @param fromActno* @param toActno* @param money*/public void transfer(String fromActno,String toActno,double money) throws MoneyNotEnoughException, AppException {//查询余额是否充足Account fromAccount = accountDao.selectBtActNo(fromActno);if(fromAccount.getBalance()<money){throw new MoneyNotEnoughException("余额不足");}//程序到这里说明余额够Account toAct=accountDao.selectBtActNo(toActno);//修改余额fromAccount.setBalance(fromAccount.getBalance()-money);toAct.setBalance(toAct.getBalance()+money);//更新数据库int count=accountDao.update(fromAccount);count += accountDao.update(toAct);//count++;if(count!=2){throw new AppException("转账异常");}}}

servlet里做的就是调度

package com.bank.mvc;import com.bank.exception.AppException;
import com.bank.exception.MoneyNotEnoughException;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 java.io.IOException;
import java.io.PrintWriter;/*** 让AcountServlet做为Controller  调度员* 负责调度其他组件* @author hrui* @date 2023/9/1 12:27*/
@WebServlet("/transfer")
public class AccountServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取前端传来的参数String fromActno = req.getParameter("fromActno");String toActno = req.getParameter("toActno");double money = Double.parseDouble(req.getParameter("money"));//调用业务方法处理业务(调度Model处理业务)AccountService accountService=new AccountService();try {accountService.transfer(fromActno,toActno,money);resp.sendRedirect(req.getContextPath()+"/success.jsp");} catch (MoneyNotEnoughException e) {e.printStackTrace();resp.sendRedirect(req.getContextPath()+"/moneynoenough.jsp");} catch (AppException e) {e.printStackTrace();resp.sendRedirect(req.getContextPath()+"/error.jsp");}}
}

三个页面显示

上面代码缺少事务控制,一般事务都在service进行控制

一般来说是在service层去开启事务提交事务

这里事务管理,做的low的方式就是在业务层获取数据库连接对象,然后传进去,当然这样做的话,在DAO层就不要在finally中关闭事务了.传个null就行,在Service中开启事务,并在Service中提交事务,在Service中的finally中关闭连接

上代码

DAO

package com.bank.mvc;import com.bank.utils.DBUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;/*** 负责Acount数据的增删改查* 1.什么是DAO*      Data Access Object(数据访问对象)* 2.DAO实际上是一种设计模式,属于JAVAEE的设计模式之一.(不是23种设计模式)* 3.DAO只负责数据库CRUD,没有任何业务逻辑* 4.没有任何业务逻辑,只负责表中数据增删改查,有一个特殊的称谓:DAO对象* @author hrui* @date 2023/9/1 12:39*/
public class AccountDao {public int insert(Account act,Connection conn){PreparedStatement ps=null;int count=0;try {String sql="insert into t_act(actno,balance) values (?,?)";ps=conn.prepareStatement(sql);ps.setString(1, act.getActno());ps.setDouble(2, act.getBalance());count=ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public int deleteByActno(Long id,Connection conn){PreparedStatement ps=null;int count=0;try {String sql="delete from t_act where id=?";ps=conn.prepareStatement(sql);ps.setLong(1, id);count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public int update(Account act,Connection conn){PreparedStatement ps=null;int count=0;try {String sql="update t_act set balance=? where id=?";ps=conn.prepareStatement(sql);ps.setDouble(1, act.getBalance());ps.setLong(2, act.getId());count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public Account selectBtActNo(String actno,Connection conn){PreparedStatement ps=null;ResultSet rs=null;Account account=new Account();try {String sql="select id,actno,balance from t_act where actno=?";ps=conn.prepareStatement(sql);ps.setString(1, actno);rs = ps.executeQuery();if(rs.next()){Long id=rs.getLong("id");String actno1=rs.getString("actno");Double balance=rs.getDouble("balance");account.setId(id);account.setActno(actno1);account.setBalance(balance);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return account;}public List<Account> selectAll(Connection conn){Connection conn=null;PreparedStatement ps=null;ResultSet rs=null;List<Account> list=new ArrayList<>();try {String sql="select id,actno,balance from t_act ";ps=conn.prepareStatement(sql);rs = ps.executeQuery();while(rs.next()){Long id=rs.getLong("id");String actno=rs.getString("actno");Double balance=rs.getDouble("balance");Account account=new Account();account.setId(id);account.setActno(actno);account.setBalance(balance);list.add(account);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return list;}
}

Service

package com.bank.mvc;import com.bank.exception.AppException;
import com.bank.exception.MoneyNotEnoughException;
import com.bank.utils.DBUtil;import java.sql.Connection;
import java.sql.SQLException;/*** Service:业务* 专门处理Account的业务处理类* 该类只专注业务处理* 主要专注于MVC模式,不需要专注于取什么名字  xxx都可以* @author hrui* @date 2023/9/2 0:49*/
public class AccountService {private AccountDao accountDao=new AccountDao();/*** 完成转账的业务逻辑* @param fromActno* @param toActno* @param money*/public void transfer(String fromActno,String toActno,double money) throws MoneyNotEnoughException, AppException {//Service层控制事务//开启事务(需要用到Connection对象)Connection conn=null;try {conn = DBUtil.getConnection();conn.setAutoCommit(false);//查询余额是否充足Account fromAccount = accountDao.selectBtActNo(fromActno,conn);if(fromAccount.getBalance()<money){throw new MoneyNotEnoughException("余额不足");}//程序到这里说明余额够Account toAct=accountDao.selectBtActNo(toActno,conn);//修改余额fromAccount.setBalance(fromAccount.getBalance()-money);toAct.setBalance(toAct.getBalance()+money);//更新数据库int count=accountDao.update(fromAccount,conn);count += accountDao.update(toAct,conn);
//        String str=null;
//        str.toString();//或者//count++;  会向用户提示转账失败  但是转账确已经完成   或者1账户减款而2账户没有加的情况if(count!=2){throw new AppException("转账异常");}conn.commit();} catch (SQLException e) {e.printStackTrace();}finally {DBUtil.close(conn,null,null);}}}

但上面代码有点low

如何解决Connection传参问题

用ThreadLocal

改造代码

DBUtil

package com.bank.utils;import java.sql.*;
import java.util.ResourceBundle;/*** @author hrui* @date 2023/9/1 10:24*/
public class DBUtil {private static ResourceBundle bundle=ResourceBundle.getBundle("resources/jdbc");private static String driver=bundle.getString("driver");private static String url=bundle.getString("url");private static String username=bundle.getString("username");private static String password=bundle.getString("password");//不让创建对象,原因工具类方法一般都静态的,无需外部创建对象//为防止外部创建对象,构造私有化private DBUtil(){}//DBUtil类加载时注册驱动static{try {Class.forName(driver);} catch (ClassNotFoundException e) {e.printStackTrace();}}private static ThreadLocal<Connection> local=new ThreadLocal<>();//没有使用连接池,直接创建的连接对象public static Connection getConnection() throws SQLException {Connection conn=local.get();if(conn==null) {conn = DriverManager.getConnection(url, username, password);local.set(conn);}return conn;}public static void close(Connection conn, Statement statement, ResultSet rs){if(rs!=null){try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if(statement!=null){try {statement.close();} catch (SQLException e) {e.printStackTrace();}}if(conn!=null){try {conn.close();//注意:关闭连接时候移除  Tomcat是支持线程池的,不从当前线程里移除 有可能下次别人拿到了,但是conn已经关闭local.remove();} catch (SQLException e) {e.printStackTrace();}}}
}

将AccountDao恢复原状,还是从DBUtil里取Connection,但是不需要再传参数,注意finally里面Connection照样传null,原因:还是需要在Service层进行事务控制

package com.bank.mvc;import com.bank.utils.DBUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;/*** 负责Acount数据的增删改查* 1.什么是DAO*      Data Access Object(数据访问对象)* 2.DAO实际上是一种设计模式,属于JAVAEE的设计模式之一.(不是23种设计模式)* 3.DAO只负责数据库CRUD,没有任何业务逻辑* 4.没有任何业务逻辑,只负责表中数据增删改查,有一个特殊的称谓:DAO对象* @author hrui* @date 2023/9/1 12:39*/
public class AccountDao {public int insert(Account act){PreparedStatement ps=null;int count=0;try {Connection  conn= DBUtil.getConnection();String sql="insert into t_act(actno,balance) values (?,?)";ps=conn.prepareStatement(sql);ps.setString(1, act.getActno());ps.setDouble(2, act.getBalance());count=ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public int deleteByActno(Long id){PreparedStatement ps=null;int count=0;try {Connection  conn= DBUtil.getConnection();String sql="delete from t_act where id=?";ps=conn.prepareStatement(sql);ps.setLong(1, id);count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public int update(Account act){PreparedStatement ps=null;int count=0;try {Connection conn=DBUtil.getConnection();String sql="update t_act set balance=? where id=?";ps=conn.prepareStatement(sql);ps.setDouble(1, act.getBalance());ps.setLong(2, act.getId());count = ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return count;}public Account selectBtActNo(String actno){PreparedStatement ps=null;ResultSet rs=null;Account account=new Account();try {Connection conn=DBUtil.getConnection();String sql="select id,actno,balance from t_act where actno=?";ps=conn.prepareStatement(sql);ps.setString(1, actno);rs = ps.executeQuery();if(rs.next()){Long id=rs.getLong("id");String actno1=rs.getString("actno");Double balance=rs.getDouble("balance");account.setId(id);account.setActno(actno1);account.setBalance(balance);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return account;}public List<Account> selectAll(){PreparedStatement ps=null;ResultSet rs=null;List<Account> list=new ArrayList<>();try {Connection conn=DBUtil.getConnection();String sql="select id,actno,balance from t_act ";ps=conn.prepareStatement(sql);rs = ps.executeQuery();while(rs.next()){Long id=rs.getLong("id");String actno=rs.getString("actno");Double balance=rs.getDouble("balance");Account account=new Account();account.setId(id);account.setActno(actno);account.setBalance(balance);list.add(account);}} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}finally {DBUtil.close(null,ps,null);}return list;}
}

业务层

package com.bank.mvc;import com.bank.exception.AppException;
import com.bank.exception.MoneyNotEnoughException;
import com.bank.utils.DBUtil;import java.sql.Connection;
import java.sql.SQLException;/*** Service:业务* 专门处理Account的业务处理类* 该类只专注业务处理* 主要专注于MVC模式,不需要专注于取什么名字  xxx都可以* @author hrui* @date 2023/9/2 0:49*/
public class AccountService {private AccountDao accountDao=new AccountDao();/*** 完成转账的业务逻辑* @param fromActno* @param toActno* @param money*/public void transfer(String fromActno,String toActno,double money) throws MoneyNotEnoughException, AppException {try(Connection conn= DBUtil.getConnection()){conn.setAutoCommit(false);//查询余额是否充足Account fromAccount = accountDao.selectBtActNo(fromActno);if(fromAccount.getBalance()<money){throw new MoneyNotEnoughException("余额不足");}//程序到这里说明余额够Account toAct=accountDao.selectBtActNo(toActno);//修改余额fromAccount.setBalance(fromAccount.getBalance()-money);toAct.setBalance(toAct.getBalance()+money);//更新数据库int count=accountDao.update(fromAccount);count += accountDao.update(toAct);
//        String str=null;
//        str.toString();//或者//count++;  会向用户提示转账失败  但是转账确已经完成   或者1账户减款而2账户没有加的情况if(count!=2){throw new AppException("转账异常");}conn.commit();} catch (SQLException e) {e.printStackTrace();throw new AppException("转账异常");}}}