J2EE基础之自定义MVC原理

目录

一、MVC简介

二、优缺点：

二、最初的增删改查

三、反射版的增删改查

四、自定义mvc后台代码实现

一、MVC简介

MVC(Model View Controller)是一种软件设计的框架模式，它采用模型(Model)-视图(View)-控制器(controller)的方法把业务逻辑、数据与界面显示分离。把众多的业务逻辑聚集到一个部件里面，当然这种比较官方的解释是不能让我们足够清晰的理解什么是MVC的。用通俗的话来讲，MVC的理念就是把数据处理、数据展示(界面)和程序/用户的交互三者分离开的一种编程

二、优缺点：

【优点】

1. 耦合性低，方便维护，可以利于分工协作

2. 重用性高

【缺点】

1. 使得项目架构变得复杂，对开发人员要求高

二、最初的增删改查

• demo1：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>







目前增删改查的方法
增加
删除
修改
查询

•  DelBookServlet：

package ps.web;

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;
@WebServlet("/book/del")
public class DelBookServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("处理书籍的 删除业务，调动BookBiz");
	}
	
}

• AddBookServlet：

package ps.web;

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;
@WebServlet("/book/add")
public class AddBookServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("处理书籍的 增加业务，调动BookBiz");
	}
	
}

• EditBookServlet：

package ps.web;

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;
@WebServlet("/book/edit")
public class EditBookServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("处理书籍的 修改业务，调动BookBiz");
	}
	
}

•  ListBookServlet：

package ps.web;

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;
@WebServlet("/book/list")
public class ListBookServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("处理书籍的 查询业务，调动BookBiz");
	}
	
}

• 运行结果：

•  存在的问题：

    1.关于单个实体/表操作场景越多，需要新建的类也就越多，

        造成了项目中类的数量过于庞大
    2.当新增了业务，除了要添加该业务对应的方法
    3.反射相关代码，在每一个实体类对应的servlet中都存在
    4.每一个servlet中都有doget、dopost

三、反射版的增删改查

尝试用一个servlet写共有的增删改查

package ps.web;

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;
@WebServlet("/book.action")
public class BookServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//	为了区分当前请求的目的，增删改查的目的，就从前台调用的方法名传递到后台
		String methodName = req.getParameter("methodName");
//		methodName可能是add/del/edit/list/load/xxx/yyy/aaa...
//		前台传递什么方法，就调用当前类的对应的方法
		try {
			Method m = this.getClass()//BookServlet.class
			.getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
			m.setAccessible(true);
			//调用当前类实例的methodName方法
			m.invoke(this, req,resp);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} 
		
		
	}
	private void load(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个servlet中调用load方法");
	}
	private void list(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个servlet中调用list方法");
	}
	private void edit(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用edit方法");
	}
	private void del(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用del方法");
	}
	private void add(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用add方法");
	}
	
}

• demo2:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>








 类数量过多问题的优化
增加
删除
修改
查看
回显

•  测试结果：

 

 

四、自定义mvc后台代码实现

最后就是解决测试类很多重复的dopost和doget方法
自定义mvc框架工作原理图

•  demo3：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>









订单类
增加
删除
修改
查看
回显

• OrderServlet：

package ps.web;

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;
@WebServlet("/order.action")
public class OrderServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//	为了区分当前请求的目的，增删改查的目的，就从前台调用的方法名传递到后台
		String methodName = req.getParameter("methodName");
//		methodName可能是add/del/edit/list/load/xxx/yyy/aaa...
//		前台传递什么方法，就调用当前类的对应的方法
		try {
			Method m = this.getClass()//BookServlet.class
			.getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
			m.setAccessible(true);
			//调用当前类实例的methodName方法
			m.invoke(this, req,resp);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} 
		
	}
	private void load(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个orderservlet中调用load方法");
	}
	private void list(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个orderservlet中调用list方法");
	}
	private void edit(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个orderservlet中调用edit方法");
	}
	private void del(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个orderservlet中调用del方法");
	}
	private void add(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个orderservlet中调用add方法");
	}
	
}

• 所用到的包类： 

新写上面framework包里的类：

• Action:

package framework;

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


public interface Action {
	void execute(HttpServletRequest req,HttpServletResponse resp);

}

• ActionSupport: （用来判断是什么请求ActionSupport.java）

package framework;

import java.lang.reflect.Method;

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

public class ActionSupport implements Action{

	@Override
	public void execute(HttpServletRequest req, HttpServletResponse resp) {
		String methodName = req.getParameter("methodName");
//		methodName可能是add/del/edit/list/load/xxx/yyy/aaa...
//		前台传递什么方法，就调用当前类的对应的方法
		try {
			Method m = this.getClass()//BookServlet.class
			.getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
			m.setAccessible(true);
			//调用当前类实例的methodName方法
			m.invoke(this, req,resp);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

• DispatherServlet: （创建一个中央控制器DispatcherServlet.java（处理所有以.action的请求））

package 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;

import ps.web.BookAction;


@WebServlet("*.action")
public class DispatherServlet extends HttpServlet{
	private Map actions =new HashMap();
	
	//程序启动时，只会加载一次
	@Override
	public void init() throws ServletException {
		actions.put("/book", new BookAction());
		actions.put("/order", new BookAction());
	}
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doGet(req, resp);
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		//http://localhost:8080/mvc/book.action?methodName=list
		String uri = req.getRequestURI();
//		要拿到/book.就是最后一个/到最后一个.的为止
		uri=uri.substring(uri.lastIndexOf("/"),uri.lastIndexOf("."));
		Action action = actions.get(uri);
		action.execute(req, resp);
	}
}

• bookAction:

package ps.web;

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

import framework.Action;
import framework.ActionSupport;

public class BookAction extends ActionSupport{

	private void load(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个servlet中调用load方法");
	}
	private void list(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("在同一个servlet中调用list方法");
	}
	private void edit(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用edit方法");
	}
	private void del(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用del方法");
	}
	private void add(HttpServletRequest req, HttpServletResponse resp) {
		System.out.println("再同一个servlet中调用add方法");
	}
	
}

• 运行结果：

 今天的知识就分享到这里啦！咱们下次再见！