JavaWeb开发技术—MVC开发模式—代码分层—0001

MVC开发模式的重要概念及在项目中的使用：

1.什么是MVC开发模式

2.为啥要使用MVC模式

3.如何在项目使用MVC模式

本文中加粗红色最好熟记 

什么是MVC开发模式：

为啥要使用MVC模式 :

       MVC是一种程序开发设计模式,它实现了显示模块与功能模块的分离、分层。它主要分模型、视图、控制器三层，其中M代表业务逻辑层，也就是软件开发的功能；V代表视图层，也就是使用什么组件显示数据，常用的就是HTML、和JSP等文件；而C代表控制层，代表软件的大方向的执行流程以及使用哪个视图对象将数据展示给用户。所以MVC就是将不同功能的组件进行隔离与分层，从而有利于程序的模块化开发、代码的后期维护。

提高了程序的可维护性、可移植性、可扩展性与可重用性，降低了程序的开发难度。

为了进一步说明使用MVC的理由：通过一个简单案例加深下印象

不使用MVC开发web项目，对代码不层的效果如何呢？

案例目录结构：（用户登录案例）

主要的演示代码：

index.jsp

<%@page language="java" import="java.util.*,java.sql.*" 
	pageEncoding="utf-8"%>
<!doctype html public "-//w3c//dtd html 4.01 Transitional//EN">
<html>
	<head>
		<title>No MVC</title>
	</head>
	<body>
		<%
			boolean isLoginSuccess = false;//逻辑标记
			//准备数据库参数
			String url = "jdbc:mysql://localhost:3306/demo";
			String driverName = "com.mysql.jdbc.Driver";
			String username = "root";
			String password = "1234";
			//加载驱动
			Class.forName(driverName);
			Connection connection = DriverManager.getConnection(url, username, password);
			//查询数据
			String sql = "select * from user where username=? and password=? ";
			PreparedStatement ps = connection.prepareStatement(sql);
			ps.setString(1, "张三");
			ps.setString(2, "111");
			ResultSet rs = ps.executeQuery();
			//逻辑判断
			while(rs.next()){
				isLoginSuccess = true;
			}
			rs.close();
			ps.close();
			connection.close();
			
			//跳转控制
			if(isLoginSuccess){
				response.sendRedirect("login?status="+1);
				
			}else{
				response.sendRedirect("no.jsp?status="+0);	
			}
		%>
	</body>
</html>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>NO-MVC-Model-001</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>login</servlet-name>
    <servlet-class>com.dk.web.UserLogin</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

ok.jsp

<%@page language="java" import="java.util.*,java.sql.*" 
	pageEncoding="utf-8"%>
<!doctype html public "-//w3c//dtd html 4.01 Transitional//EN">
<html>
	<head>
		<title>No MVC-ok</title>
	</head>
	<body>
		<h1>ok</h1>
	</body>
</html>

no.jsp

<%@page language="java" import="java.util.*,java.sql.*" 
	pageEncoding="utf-8"%>
<!doctype html public "-//w3c//dtd html 4.01 Transitional//EN">
<html>
	<head>
		<title>No MVC-no</title>
	</head>
	<body>
		<h1>no</h1>
		状态值：<h2><%=request.getParameter("status") %></h2>
	</body>
</html>

UserLogin.java

package com.dk.web;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class UserLogin extends HttpServlet {
	
	@Override
	protected void service(HttpServletRequest req,
			HttpServletResponse resp) throws ServletException, IOException {
			System.out.println("service========================>>>>>>>>>>>>>>>");
			System.out.println(req.getParameter("status"));
			
			req.setAttribute("user", "Jack");
			req.getRequestDispatcher("/WEB-INF/index.jsp").forward(req, resp);
			
	}

}

加载项目到Tomcat后，启动Tomcat运行程序：

录入请求路径：http://localhost:8080/NO-MVC-Model-001/login

如果没有异常并且查询到用户记录后,页面效果：

如果存在异常或没有用户记录，页面效果：

你会发现,以上开发代码login.jsp中里面包含很多功能的代码，这样设计虽然在软件开发初期使项目的开发进度加快。但后期的维护量非常庞大，开发中需求变更时代码的修改也很吃力，所以的功能代码混杂在一起就像一团乱麻。所以就要对代码进行分层，

M层使用JavaBean服务组件，V层可以使用JSP文件只显示数据， C层可以使用Servlet或其他的框架组件。

 

---

 使用MVC构建的项目目录结构：

具体代码细节：

Userinfo.java

package entity;
public class Userinfo {

	private String id;
	private String username;
	private String password;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

}

GetConnection.java

package dbtools;

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

public class GetConnection {

	public static Connection getConnectionFromJDBC()
			throws ClassNotFoundException, SQLException {

		String url = "jdbc:mysql://localhost:3306/demo";
		String driverName = "com.mysql.jdbc.Driver";
		String username = "root";
		String password = "1234";

		Class.forName(driverName);
		Connection connection = DriverManager.getConnection(url, username,
				password);
		return connection;
	}

	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		System.out.println(getConnectionFromJDBC());
	}
}

UserinfoDao.java

package dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import dbtools.GetConnection;
import entity.Userinfo;

public class UserinfoDao {

	public Userinfo findUserinfo(String username, String password)
			throws SQLException, ClassNotFoundException {
		System.out.println("DAO________findUserinfo_____"+username+":"+password+"________>>>>>");
		Userinfo userinfo = null;
		String sql = "SELECT * FROM USER WHERE username=? AND PASSWORD=?";
		Connection connection = GetConnection.getConnectionFromJDBC();
		PreparedStatement ps = connection.prepareStatement(sql);
		ps.setString(1, username);
		ps.setString(2, password);
		ResultSet rs = ps.executeQuery();
		
		while (rs.next()) {
			String iddb = rs.getString("id");
			String usernamedb = rs.getString("username");
			String passworddb = rs.getString("password");

			userinfo = new Userinfo();
			userinfo.setId(iddb);
			userinfo.setUsername(usernamedb);
			userinfo.setPassword(passworddb);

		}
		rs.close();
		ps.close();
		connection.close();

		return userinfo;
	}
}

UserinfoService.java

import java.sql.SQLException;

import dao.UserinfoDao;

public class UserinfoService {

	public boolean login(String username, String password) throws SQLException,
			ClassNotFoundException {
		UserinfoDao userinfoDao = new UserinfoDao();
		if (userinfoDao.findUserinfo(username, password) == null) {
			return false;
		} else {
			return true;
		}
	}

}

login.java

package controller;

import java.io.IOException;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import service.UserinfoService;

public class login extends HttpServlet {

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		System.out.println("doPost===============================>>>>>>>>>>");
		request.setCharacterEncoding("utf-8");
		try {
			String username = request.getParameter("username");
			String password = request.getParameter("password");
			
			UserinfoService usRef = new UserinfoService();
			if (usRef.login(username, password) == true) {
				response.sendRedirect("ok.jsp");
			} else {
				response.sendRedirect("no.jsp");
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>login</servlet-name>
    <servlet-class>controller.login</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
	<head>
	</head>
	<body>
		<form action="login" method="post">
			username:
			<input type="text" name="username">
			<br />
			password:
			<input type="text" name="password">
			<br />
			<input type="submit" value="登陆">
		</form>
	</body>
</html>

no.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
	<body>
		no.jsp
	</body>
</html>

ok.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
	<body>
		ok.jsp
	</body>
</html>

运行项目工程后：

1.如果一切正常，页面效果：

2.如果存在异常或无记录,页面效果：