MVC架构代码简单演示

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代码演示如下

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package com.xiaoguan.bank.exceptions;

public class AppException extends Exception{
    public AppException() {
        super();
    }

    public AppException(String message) {
        super(message);
    }
}

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package com.xiaoguan.bank.exceptions;

public class MoneyNotEnough extends Exception{
    public MoneyNotEnough() {
        super();
    }

    public MoneyNotEnough(String message) {
        super(message);
    }
}

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package com.xiaoguan.bank.exceptions;

public class MoneyNotEnough extends Exception{
    public MoneyNotEnough() {
        super();
    }

    public MoneyNotEnough(String message) {
        super(message);
    }
}

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package com.xiaoguan.bank.mvc;

import com.xiaoguan.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;

public class AccountDao {//负责数据处理，Data Access Object数据访问对象,一般情况一张表对应一个DAO

    public 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) {
            throw new RuntimeException(e);
        }finally {
            DBUtil.close(null,ps,null);
        }
        return count;
    }
    public int deleteById(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) {
            throw new RuntimeException(e);
        }finally {
            DBUtil.close(null,ps,null);
        }
        return count;
    }
    public int update(Account account){
        Connection conn=null;
        PreparedStatement ps=null;
        int count=0;
        try {
            conn = DBUtil.getConnection();
            String sql="update t_act set balance=?,actno=? where id=?";
            ps=conn.prepareStatement(sql);
            ps.setDouble(1,account.getBalance());
            ps.setString(2,account.getActno());
            ps.setLong(3,account.getId());
            count=ps.executeUpdate();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            DBUtil.close(null,ps,null);
        }
        return count;
    }
    public Account selectByActno(String actno){
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        Account account=new Account();
        try {
            conn = DBUtil.getConnection();
            String sql="select id,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");
                Double balance=rs.getDouble("balance");
                account.setActno(actno);
                account.setId(id);
                account.setBalance(balance);
            }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            DBUtil.close(null,ps,rs);
        }
        return account;
    }
    public List<Account> selectAll(){
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        List<Account> accounts=new ArrayList<>();
        try {
            conn = DBUtil.getConnection();
            String sql="select id,balance,actno from t_act ";
            ps=conn.prepareStatement(sql);
            rs=ps.executeQuery();
            while(rs.next()){
                Long id= rs.getLong("id");
                Double balance=rs.getDouble("balance");
                String actno=rs.getString("actno");
                accounts.add(new Account(id,actno,balance));
            }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            DBUtil.close(null,ps,rs);
        }
        return accounts;
    }
}

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package com.xiaoguan.bank.mvc;

import com.xiaoguan.bank.exceptions.AppException;
import com.xiaoguan.bank.exceptions.MoneyNotEnough;
import com.xiaoguan.bank.utils.DBUtil;

import java.sql.Connection;
import java.sql.SQLException;

public class AccountService {
    Connection conn=null;
    private AccountDao accountDao=new AccountDao();
    public void transfer(String fromActno,String toActno,double money) throws MoneyNotEnough, AppException {    //完成转账逻辑
        try{
            conn=DBUtil.getConnection();
            conn.setAutoCommit(false);
            Account fromAccount = accountDao.selectByActno(fromActno);
            if(fromAccount.getBalance()<money){
                throw new MoneyNotEnough("对不起，余额不足");
            }
            Account toAccount=accountDao.selectByActno(toActno);
            fromAccount.setBalance(fromAccount.getBalance()-money);
            toAccount.setBalance(toAccount.getBalance()+money);
            int count=accountDao.update(fromAccount);
            count+=accountDao.update(toAccount);
            if (count!=2) {
                throw new AppException("转账出错了");
            }
            conn.commit();
        }catch(SQLException e){
            if (conn!=null){
                try {
                    conn.rollback();
                } catch (SQLException ex) {
                    e.printStackTrace();
                }
            }
            throw new AppException("转账出错了");
        }catch (Exception e){
            if (conn!=null){
                try {
                    conn.rollback();
                } catch (SQLException ex) {
                    e.printStackTrace();
                }
            }
            throw new AppException("转账出错了");
        }finally {
            DBUtil.close(conn,null,null);
        }
    }
}

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package com.xiaoguan.bank.mvc;

import com.xiaoguan.bank.exceptions.AppException;
import com.xiaoguan.bank.exceptions.MoneyNotEnough;
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;
@WebServlet("/transfer")
public class AccountServlet extends HttpServlet {//作为Controller
    AccountService accountService=new AccountService();
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String fromActno = request.getParameter("fromActno");
        String toActno = request.getParameter("toActno");
        double money = Double.parseDouble(request.getParameter("money"));

        try {
            accountService.transfer(fromActno,toActno,money);
            response.sendRedirect(request.getContextPath()+"/success.jsp");
        } catch (MoneyNotEnough e) {
            response.sendRedirect(request.getContextPath()+"/moneyNotEnough.jsp");
        } catch (Exception e) {
            response.sendRedirect(request.getContextPath()+"/error.jsp");
        }
    }
}

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package com.xiaoguan.bank.utils;

import java.sql.*;
import java.util.ResourceBundle;

public class DBUtil {
    private 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");
    static {
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    private static ThreadLocal<Connection> local=new ThreadLocal<>();
    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, PreparedStatement ps, ResultSet rs){
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if (ps != null) {
            try {
                ps.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if (conn != null) {
            try {
                conn.close();
                local.remove();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

该程序还右许多缺陷，比如并没有考虑并发的情况,自己转自己和多人访问会有错误,还有没有写出各部分相对应的接口来，这些都做了才相对规范。

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driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/mvc
username=root
password=密码
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<%--
  Created by IntelliJ IDEA.
  User: xiaoguan
  Date: 2023/5/24
  Time: 20:28
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>转账失败</title>
</head>
<body>
  <h1>转账失败</h1>
</body>
</html>

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<%--
  Created by IntelliJ IDEA.
  User: xiaoguan
  Date: 2023/5/24
  Time: 14:22
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <base href="${pageContext.request.scheme}://${pageContext.request.serverName}:${pageContext.request.serverPort}/${pageContext.request.contextPath}/">
    <title>银行账户转账</title>
  </head>
  <body>
      <form action="transfer" method="post">
          转出账号：<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>

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<%--
  Created by IntelliJ IDEA.
  User: xiaoguan
  Date: 2023/5/24
  Time: 20:31
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>余额不足</title>
</head>
<body>
<h1>余额不足，转账失败</h1>
</body>
</html>

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<%--
  Created by IntelliJ IDEA.
  User: xiaoguan
  Date: 2023/5/24
  Time: 20:28
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>转账成功</title>
</head>
<body>
  <h1>转账成功</h1>
</body>
</html>