目录
- 一、MVC
- 二、MVC的演变
- 2.1 极易MVC
- Controller层——Servlet
- view层——JSP
- 缺点：Servlet过多、代码冗余
- 2.2 简易MVC
- Controller层——Servlet
- view层——JSP
- 缺点：在Servlet中if语句冗余
- 2.3普易MVC
- Controller层——Servlet
- view层——JSP
- 缺点：反射代码重复
- 三、MVC架构模式的初实现
- 3.1 工作流程图
- 3.2 实现
- Controller层——Servlet
- 中央控制器
- 子控制器
- 具体Action类
- view层——JSP
一、MVC
MVC（Model View Controller）是一种软件工程中的一种软件架构模式，把软件系统分为三个基本部分：
- 模型（Model）
- 视图（View）
- 控制器（Controller）
详细介绍在这里——>MVC详解
二、MVC的演变
为了更加方便地直观看出MVC的演变，在这里我省略Model层，只写View——JSP和Controller——Servlet
2.1 极易MVC
Controller层——Servlet
这里写4个极易Servlet，crud
package com.xqx.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;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/bookAdd.action")
public class BookAddServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("add");
}
}
package com.xqx.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;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/bookDel.action")
public class BookDelServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("del");
}
}
package com.xqx.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;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/bookUpd.action")
public class BookUpdServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("upd");
}
}
package com.xqx.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;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/bookList.action")
public class BookListServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("list");
}
}
view层——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>
<h1>极易MVC</h1>
<a href="bookAdd.action">新增</a>
<a href="bookDel.action">删除</a>
<a href="bookUpd.action">修改</a>
<a href="bookList.action">查看</a>
</body>
</html>
运行后的Jsp，点击哪个链接就跳哪个Servlet
，
点击修改和查看后，进入了对应的Servlet，打印结果
缺点：Servlet过多、代码冗余
但是这样我们也能非常直观地看出这么写的缺点，每写一个方法就要写一个Servlet，要是我有100个实体，每个实体都要增删改查的话，那么不是要写400个Servler，这样代码量太大了，并且还有很多重复代码。
2.2 简易MVC
用极易MVC Servlet会过多的话，那我们做个通用Servlet不就行了
Controller层——Servlet
通用的Servlet，判断jsp传来的参数即可回显不同内容
package com.xqx.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;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/book.action")
public class BookServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 拿到jsp传来的method
String method = request.getParameter("method");
if (method.equals("add")) {
add(request,response);
} else if (method.equals("del")) {
del(request,response);
} else if (method.equals("upd")) {
upd(request,response);
} else if (method.equals("list")) {
list(request,response);
}
}
private void list(HttpServletRequest request, HttpServletResponse response) {
System.out.println("list");
}
private void upd(HttpServletRequest request, HttpServletResponse response) {
System.out.println("upd");
}
private void del(HttpServletRequest request, HttpServletResponse response) {
System.out.println("del");
}
private void add(HttpServletRequest request, HttpServletResponse response) {
System.out.println("add");
}
view层——JSP
在href路径加方法参数即可
<%@ 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>
<h1>极易MVC</h1>
<a href="bookAdd.action">新增</a>
<a href="bookDel.action">删除</a>
<a href="bookUpd.action">修改</a>
<a href="bookList.action">查看</a>
<h1>简易MVC</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
</body>
</html>
打印结果：
缺点：在Servlet中if语句冗余
虽然只要写一个Servlet了，但是如果有100个需求100个方法呢，难道写100个if语句？代码量不也是很大么，那么怎么解决呢？
2.3普易MVC
在简易MVC中如果方法越多，Servlet中if语句也会越来越多，要是能有一个技术能拿到所有方法就好了，那么你想到这个技术是什么了吗？
没错，就是反射！！！
Controller层——Servlet
package com.xqx.servlet;
import java.io.IOException;
import java.lang.reflect.Method;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class BookAddServlet
*/
@WebServlet("/book.action")
public class BookServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 拿到jsp传来的method
String method = request.getParameter("method");
try {
//拿到HttpServletRequest、HttpServletResponse类型的方法
Method m = this.getClass().getDeclaredMethod(method, HttpServletRequest.class, HttpServletResponse.class);
//打开访问权限
m.setAccessible(true);
//调用方法
m.invoke(this, request,response);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private void list(HttpServletRequest request, HttpServletResponse response) {
System.out.println("list");
}
private void upd(HttpServletRequest request, HttpServletResponse response) {
System.out.println("upd");
}
private void del(HttpServletRequest request, HttpServletResponse response) {
System.out.println("del");
}
private void add(HttpServletRequest request, HttpServletResponse response) {
System.out.println("add");
}
}
view层——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>
<h1>极易MVC</h1>
<a href="bookAdd.action">新增</a>
<a href="bookDel.action">删除</a>
<a href="bookUpd.action">修改</a>
<a href="bookList.action">查看</a>
<hr>
<h1>简易MVC</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
<hr>
<h1>普易MVC</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
</body>
</html>
打印结果：
缺点：反射代码重复
虽然它能通过反射拿到所有的方法，减少了if语句的冗余，但是我们将视角上升到整个项目，一个项目不可能只有一个实体类吧，那Servlet也不是只有一个，但每个类对应的Servlet拿到所有方法的反射代码是一样的呀，这个代码重复，能否有一个真正意义上面对所有类的通用Servlet呢？
没有咱就写一个嘛，对吧，写一个能处理所有前端发送过来请求的Servlet，其实这个Servlet就是MVC中的中央控制器，到了这里其实已经有了MVC架构模式的雏形了。
三、MVC架构模式的初实现
3.1 工作流程图
3.2 实现
- 创建一个能处理所有前端发送过来请求的Servle，即中央控制器，拿到所有方法的反射代码就在这里，并根据请求的类型调用相应的业务逻辑（去子控制器）
- 创建一个子控制器，用于处理特定的用户请求或操作，这是真正处理用户请求的Servlet
- 创建一个定义方法的Servlet，继承子控制器，供子控制器调用方法
Controller层——Servlet
中央控制器
package com.xqx.framework;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/** 中央控制器 即工作流程图中的ActionServlet
* @author W许潜行
* 2023年6月29日 下午8:10:04
*/
@WebServlet("*.action")
public class DispatherServlet extends HttpServlet {
Map<String,Action> mapAction=new HashMap<>();
/**
* 初始化方法
*/
public void init() throws ServletException {
mapAction.put("/book", new BookAction());
super.init();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//得到传过来的路径名
String uri = request.getRequestURI();// /J2EE_MVC/book.action
//得到请求的类
uri = uri.substring(uri.lastIndexOf("/"), uri.lastIndexOf("."));// /book
//拿到对应的action
Action action = mapAction.get(uri);
//调用方法
action.execute(request, response);
}
}
当有请求进入时，我们首先获取请求的URI，并从中获取类似"/book"的路径名。然后，我们使用这个路径名作为键在mapAction中查找对应的Action对象。最后，执行该Action的execute方法来处理请求。
这个DispatcherServlet类的目的是根据传入的请求路径来分发请求给不同的Action类处理，通过这种方式实现请求的路由和控制，实现了基本的MVC模式。
子控制器
package com.xqx.framework;
import java.io.IOException;
import java.lang.reflect.Method;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 字控制器，真正处理请求的类
*
*
* @author W许潜行 2023年6月29日 下午8:17:41
*/
public class Action {
public void execute(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 拿到jsp传来的method
String method = request.getParameter("method");
try {
Method m = this.getClass().getDeclaredMethod(method, HttpServletRequest.class, HttpServletResponse.class);
m.setAccessible(true);
m.invoke(this, request, response);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
这个Action类的作用是通过反射机制根据传入的method参数值来调用具体的方法进行请求处理。每个实际的Action类都可以继承这个基类，并重写具体的方法来实现自己的业务逻辑。
具体Action类
package com.xqx.framework;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**定义crud方法
* @author W许潜行
* 2023年6月29日 下午8:55:46
*/
public class BookAction extends Action{
public void list(HttpServletRequest request, HttpServletResponse response) {
System.out.println("list");
}
public void upd(HttpServletRequest request, HttpServletResponse response) {
System.out.println("upd");
}
public void del(HttpServletRequest request, HttpServletResponse response) {
System.out.println("del");
}
public void add(HttpServletRequest request, HttpServletResponse response) {
System.out.println("add");
}
}
view层——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>
<h1>极易MVC</h1>
<a href="bookAdd.action">新增</a>
<a href="bookDel.action">删除</a>
<a href="bookUpd.action">修改</a>
<a href="bookList.action">查看</a>
<hr>
<h1>简易MVC</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
<hr>
<h1>普易MVC</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
</body>
<h1>MVC架构初实现</h1>
<a href="book.action?method=add">新增</a>
<a href="book.action?method=del">删除</a>
<a href="book.action?method=upd">修改</a>
<a href="book.action?method=list">查看</a>
</body>
</html>
打印结果：
初步实现MVC架构就基本完成了，但还有很多优化之处，等之后博客再进行优化与分享。
好啦，今天的分享就到此为止！希望你看完本篇文章有所收获，祝你变得更强！！!
