• 自定义MVC原理

    目录

    一、MVC简介

    二、最初的增删改查

    三、反射版的增删改查

    四、自定义MVC工作原理图

    五、自定义MVC后台代码实现

    一、MVC简介

       1、什么是MVC？

                MVC的全名是Model View Controller，是模型(model)－视图(view)－控制器(controller)的缩写，是一种软件设计典范。它是用一种业务逻辑、数据与界面显示分离的方法来组织代码，将众多的业务逻辑聚集到一个部件里面，在需要改进和个性化定制界面及用户交互的同时，不需要重新编写业务逻辑，达到减少编码的时间。

        2、MVC的好处

            视图层和业务层分离，这样就允许更改视图层代码而不用重新编译模型和控制器代码，同样，一个应用的业务流程或者业务规则的改变只需要改动MVC的模型层即可。因为模型与控制器和视图相分离，所以很容易改变应用程序的数据层和业务规则。

    二、最初的增删改查

           jsp界面

    1. <%@ page language="java" contentType="text/html; charset=UTF-8"
    2.     pageEncoding="UTF-8"%>
    3. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    4. <html>
    5. <head>
    6. <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    7. <title>Insert title here</title>
    8. </head>
    9. <body>
    10. <h3>目前增删改查的方法</h3>
    11. <a href="${pageContext.request.contextPath }/book/add">增加</a>
    12. <a href="${pageContext.request.contextPath }/book/del">删除</a>
    13. <a href="${pageContext.request.contextPath }/book/edit">修改</a>
    14. <a href="${pageContext.request.contextPath }/book/list">查询</a>
    15. </body>
    16. </html>

    删除的Servlet

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.annotation.WebServlet;
    7. import javax.servlet.http.HttpServlet;
    8. import javax.servlet.http.HttpServletRequest;
    9. import javax.servlet.http.HttpServletResponse;
    10. @WebServlet("/book/del")
    11. public class DelBookServlet extends HttpServlet{
    12. 	@Override
    13. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    14. 		doPost(req, resp);
    15. 	}
    16. 	
    17. 	@Override
    18. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    19. 		System.out.println("处理书籍的删除业务，调用bookbiz");
    20. 	}
    21. }

     增加Servlet

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.annotation.WebServlet;
    7. import javax.servlet.http.HttpServlet;
    8. import javax.servlet.http.HttpServletRequest;
    9. import javax.servlet.http.HttpServletResponse;
    10. @WebServlet("/book/list")
    11. public class AddBookServlet extends HttpServlet{
    12. 	@Override
    13. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    14. 		doPost(req, resp);
    15. 	}
    16. 	
    17. 	@Override
    18. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    19. 		System.out.println("处理书籍的查询业务，调用bookbiz");
    20. 	}
    21. }

    修改Servlet

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.annotation.WebServlet;
    7. import javax.servlet.http.HttpServlet;
    8. import javax.servlet.http.HttpServletRequest;
    9. import javax.servlet.http.HttpServletResponse;
    10. @WebServlet("/book/edit")
    11. public class EditBookServlet extends HttpServlet{
    12. 	@Override
    13. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    14. 		doPost(req, resp);
    15. 	}
    16. 	
    17. 	@Override
    18. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    19. 		System.out.println("处理书籍的修改业务，调用bookbiz");
    20. 	}
    21. }

    查询Servlet 

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.annotation.WebServlet;
    7. import javax.servlet.http.HttpServlet;
    8. import javax.servlet.http.HttpServletRequest;
    9. import javax.servlet.http.HttpServletResponse;
    10. @WebServlet("/book/add")
    11. public class ListBookServlet extends HttpServlet{
    12. 	@Override
    13. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    14. 		doPost(req, resp);
    15. 	}
    16. 	
    17. 	@Override
    18. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    19. 		System.out.println("处理书籍的增加业务，调用bookbiz");
    20. 	}
    21. }

    界面效果

    点击标签控制台弹出对应的Servlet

     

     

     从最初的增删改查可以看到问题：

          1、 如果关于单个实体/表操作场景越多，需要新建的类也就越多，也就造成了项目中类的数量过于庞大

    三、反射版的增删改查

                   jsp界面：

    1. <%@ page language="java" contentType="text/html; charset=UTF-8"
    2.     pageEncoding="UTF-8"%>
    3. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    4. <html>
    5. <head>
    6. <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    7. <title>Insert title here</title>
    8. </head>
    9. <body>
    10. <h3>目前增删改查的方法</h3>
    11. <a href="${pageContext.request.contextPath }/book/add">增加</a>
    12. <a href="${pageContext.request.contextPath }/book/del">删除</a>
    13. <a href="${pageContext.request.contextPath }/book/edit">修改</a>
    14. <a href="${pageContext.request.contextPath }/book/list">查询</a>
    15.  
    16. <h3>类数量过多问题的优化</h3>
    17. <a href="${pageContext.request.contextPath }/book.action?methodName=add">增加</a>
    18. <a href="${pageContext.request.contextPath }/book.action?methodName=del">删除</a>
    19. <a href="${pageContext.request.contextPath }/book.action?methodName=edit">修改</a>
    20. <a href="${pageContext.request.contextPath }/book.action?methodName=list">查询</a>
    21. <a href="${pageContext.request.contextPath }/book.action?methodName=load">回显</a>
    22. </body>
    23. </html>

    新建一个BookServlet

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4. import java.lang.reflect.Method;
    5.  
    6. import javax.servlet.ServletException;
    7. import javax.servlet.annotation.WebServlet;
    8. import javax.servlet.http.HttpServlet;
    9. import javax.servlet.http.HttpServletRequest;
    10. import javax.servlet.http.HttpServletResponse;
    11. @WebServlet("/book.action")
    12. public class BookServlet extends HttpServlet{
    13. 	@Override
    14. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    15. 		doPost(req, resp);
    16. 	}
    17. 	
    18. 	@Override
    19. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    20. //		为了区分当前请求的目的，增删改查的目的，就从前台将要调用的方法名传递到后台
    21. 		String methodName = req.getParameter("methodName");
    22. //	
    23. 		if("add".equals(methodName)) {
    24. //			如果前台传递到后台的是一个新增的请求，那么后台就调用新增方法
    25. 			add(req,resp);
    26. 		}
    27. 		else if("del".equals(methodName)) {
    28. 			del(req,resp);
    29. 		}
    30. 		else if("edit".equals(methodName)) {
    31. 			edit(req,resp);
    32. 		}
    33. 		else if("list".equals(methodName)) {
    34. 			list(req,resp);
    35. 		}
    36. 	}
    37.  
    38. 	private void list(HttpServletRequest req, HttpServletResponse resp) {
    39. 		System.out.println("在同样一个Servlet中调用list方法");
    40. 		
    41. 	}
    42.  
    43. 	private void edit(HttpServletRequest req, HttpServletResponse resp) {
    44. 		System.out.println("在同样一个Servlet中调用edit方法");
    45. 	}
    46.  
    47. 	private void del(HttpServletRequest req, HttpServletResponse resp) {
    48. 		System.out.println("在同样一个Servlet中调用del方法");	
    49. 	}
    50.  
    51. 	private void add(HttpServletRequest req, HttpServletResponse resp) {
    52. 		System.out.println("在同样一个Servlet中调用add方法");
    53. 	}
    54. 	private void load(HttpServletRequest req, HttpServletResponse resp) {
    55. 		System.out.println("在同样一个Servlet中调用load方法");
    56. 	}
    57. }

    运行结果

     

    在上面又有一个问题：

    2、当新增了业务，除了要添加该业务对应的方法（load），同时还要改动原有的方法

    所以我们在这里优化BookServlet：

    1. package com.zwc.web;
    2.  
    3. import java.io.IOException;
    4. import java.lang.reflect.Method;
    5.  
    6. import javax.servlet.ServletException;
    7. import javax.servlet.annotation.WebServlet;
    8. import javax.servlet.http.HttpServlet;
    9. import javax.servlet.http.HttpServletRequest;
    10. import javax.servlet.http.HttpServletResponse;
    11. @WebServlet("/book.action")
    12. public class BookServlet extends HttpServlet{
    13. 	@Override
    14. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    15. 		doPost(req, resp);
    16. 	}
    17. 	
    18. 	@Override
    19. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    20. //		为了区分当前请求的目的，增删改查的目的，就从前台将要调用的方法名传递到后台
    21. 		String methodName = req.getParameter("methodName");
    22. //		methodName可以是add/del/list/edit/.....
    23. //		前台传递上面方法，就调用当前类的对应方法
    24. 		try {
    25. 			Method m = this.getClass()//BookSerlvet.class
    26. 				.getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
    27. 			m.setAccessible(true);
    28. //			调用当前类实例的methodName 方法
    29. 			m.invoke(this, req,resp);
    30. 		} catch (Exception e) {
    31. 			e.printStackTrace();
    32. 		}
    33. 		
    34. 	}
    35.  
    36. 	private void list(HttpServletRequest req, HttpServletResponse resp) {
    37. 		System.out.println("在同样一个Servlet中调用list方法");
    38. 		
    39. 	}
    40.  
    41. 	private void edit(HttpServletRequest req, HttpServletResponse resp) {
    42. 		System.out.println("在同样一个Servlet中调用edit方法");
    43. 	}
    44.  
    45. 	private void del(HttpServletRequest req, HttpServletResponse resp) {
    46. 		System.out.println("在同样一个Servlet中调用del方法");	
    47. 	}
    48.  
    49. 	private void add(HttpServletRequest req, HttpServletResponse resp) {
    50. 		System.out.println("在同样一个Servlet中调用add方法");
    51. 	}
    52. 	private void load(HttpServletRequest req, HttpServletResponse resp) {
    53. 		System.out.println("在同样一个Servlet中调用load方法");
    54. 	}
    55. }

    同样测试运行:

     

     

    若我们在增加一个订单的增删改查，同样写一个orderServlet

     

    我们可以观察到

     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Servlets中都有doget、dopost

    四、自定义MVC工作原理图

     

    五、自定义MVC后台代码实现

    先创建中央控制器：
    主要职能：接受浏览器请求，找到对应的处理人

    1. package com.zwc.framework;
    2.  
    3. import java.io.IOException;
    4. import java.util.HashMap;
    5. import java.util.Map;
    6.  
    7. import javax.servlet.ServletException;
    8. import javax.servlet.annotation.WebServlet;
    9. import javax.servlet.http.HttpServlet;
    10. import javax.servlet.http.HttpServletRequest;
    11. import javax.servlet.http.HttpServletResponse;
    12.  
    13. import com.zwc.web.BookAction;
    14.  
    15. /**
    16.  * 中央控制器：
    17.  * 主要职能：接受浏览器请求，找到对应的处理人
    18.  * @author Administrator
    19.  *
    20.  */
    21. @WebServlet("*.action")
    22. public class DispatcherServlet extends HttpServlet{
    23. 	private Map<String,Action> actions = new HashMap<String,Action>();
    24. 	
    25. //	程序启动时，只会加载一次
    26. 	@Override
    27. 	public void init() throws ServletException {
    28. 		actions.put("/book",new BookAction());
    29. 		actions.put("/order",new BookAction());
    30. 	}
    31. 	@Override
    32. 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    33. 		doPost(req, resp);
    34. 	}
    35. 	@Override
    36. 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    37. 		//http://localhost:8080/mvc/book.action?methodName=list
    38. 		String uri = req.getRequestURI();
    39. //		要拿到book，最后一个/到最后一个.为止
    40. 		 uri = uri.substring(uri.lastIndexOf("/"), uri.lastIndexOf("."));
    41. 		 Action action = actions.get(uri);
    42. 		 action.execute(req, resp);
    43. 	}
    44. }

    在创建一个子控制器，对应请求的处理人

    1. package com.zwc.framework;
    2.  
    3. import javax.servlet.http.HttpServletRequest;
    4. import javax.servlet.http.HttpServletResponse;
    5.  
    6. /**
    7.  * 子控制器：
    8.  * 对应请求的处理人
    9.  * @author Administrator
    10.  *
    11.  */
    12. public interface Action {
    13. 	void execute(HttpServletRequest req, HttpServletResponse resp); 
    14. }

    实现子控制器接口 

    1. package com.zwc.framework;
    2.  
    3. import java.lang.reflect.Method;
    4.  
    5. import javax.servlet.http.HttpServletRequest;
    6. import javax.servlet.http.HttpServletResponse;
    7.  
    8. public class ActionSupport implements Action{
    9.  
    10. 	@Override
    11. 	public void execute(HttpServletRequest req, HttpServletResponse resp) {
    12. //		为了区分当前请求的目的，增删改查的目的，就从前台将要调用的方法名传递到后台
    13. 		String methodName = req.getParameter("methodName");
    14. //		methodName可以是add/del/list/edit/.....
    15. //		前台传递上面方法，就调用当前类的对应方法
    16. 		try {
    17. 			Method m = this.getClass()//BookSerlvet.class
    18. 				.getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
    19. 			m.setAccessible(true);
    20. //			调用当前类实例的methodName 方法
    21. 			m.invoke(this, req,resp);
    22. 		} catch (Exception e) {
    23. 			e.printStackTrace();
    24. 		}
    25. 	}
    26.  
    27. }

    继承实现子控制器的接口

    1. package com.zwc.web;
    2.  
    3. import javax.servlet.http.HttpServletRequest;
    4. import javax.servlet.http.HttpServletResponse;
    5.  
    6. import com.zwc.framework.Action;
    7. import com.zwc.framework.ActionSupport;
    8.  
    9. public class BookAction extends ActionSupport{
    10.  
    11. 	private void list(HttpServletRequest req, HttpServletResponse resp) {
    12. 		System.out.println("在同样一个Servlet中调用list方法");
    13. 		
    14. 	}
    15.  
    16. 	private void edit(HttpServletRequest req, HttpServletResponse resp) {
    17. 		System.out.println("在同样一个Servlet中调用edit方法");
    18. 	}
    19.  
    20. 	private void del(HttpServletRequest req, HttpServletResponse resp) {
    21. 		System.out.println("在同样一个Servlet中调用del方法");	
    22. 	}
    23.  
    24. 	private void add(HttpServletRequest req, HttpServletResponse resp) {
    25. 		System.out.println("在同样一个Servlet中调用add方法");
    26. 	}
    27. 	private void load(HttpServletRequest req, HttpServletResponse resp) {
    28. 		System.out.println("在同样一个Servlet中调用load方法");
    29. 	}
    30.  
    31. }

    运行结果：

     

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  • 原文地址：https://blog.csdn.net/qq_65345936/article/details/125456229