程序博客网 > 二维数组元素的排序 c

MVC演化、理解

来源：互联网 发布：二维数组元素的排序 c 编辑：程序博客网 时间：2024/06/04 18:54

我们先不解释什么叫MVC，针对项目中的问题，解决推进慢慢把项目改进发展成MVC来理解它。

无论是jsp中嵌入java代码，或者servlet内嵌html都会使代码混乱，不便分工合作和后期开发。我们现在让jsp只负责显示，而代码控制给servlet负责，就是处理请求交给servlet，这样我们就把项目的显示和控制分离开来。

以用户注册作为例子，首先要有页面register.jsp输入用户信息，因为jsp只负责显示，所以前面要有一个servlet(register.do)控制跳转到register.jsp页面，然后视图提交给另一个servlet(user_add.do)进行用户添加，再跳转到用户列表(user_list.jsp)页面，同样要用servlet(user_list.do)控制。（如果没有user_list.do，让user_add.do把user_list.do做的事给做了，除了职责不单一，还会有重复提交的隐患另作处理，如果不用服务器端跳转用客户端跳转，如果把jsp文件放在WEB-INF是找不到的），即

register.do--------forword()------>register.jsp------------submit()-------->user_add.do-------------redirect()------>user_list.do---------forword()------>user_list.jsp

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">    <servlet>    <servlet-name>UserRegister</servlet-name>    <servlet-class>com.yan.mvc.servlet.UserRegister</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>UserRegister</servlet-name>    <url-pattern>/register.do</url-pattern>  </servlet-mapping>    <servlet>    <servlet-name>UserAdd</servlet-name>    <servlet-class>com.yan.mvc.servlet.UserAdd</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>UserAdd</servlet-name>    <url-pattern>/user_add.do</url-pattern>  </servlet-mapping>     <servlet>    <servlet-name>UserList</servlet-name>    <servlet-class>com.yan.mvc.servlet.UserList</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>UserList</servlet-name>    <url-pattern>/user_list.do</url-pattern>  </servlet-mapping></web-app>

register.do

package com.yan.mvc.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;public class UserRegister extends HttpServlet {private static final long serialVersionUID = 1L;              public UserRegister() {        super();           }protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getRequestDispatcher("/WEB-INF/user/register.jsp").forward(request, response);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}
register.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><form action="user_add.do" method="post"><table align="center" width="500" border="1"><tr><td>用户名称：</td><td><input type="text" name="name" value=""/></td></tr><tr><td>用户年龄：</td><td><input type="text" name="age" value=""/></td></tr><tr><td colspan="2"><input type="submit" value="添加用户"></td></tr></table></form></body></html>
user_add.do
package com.yan.mvc.servlet;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yan.mvc.model.User;public class UserAdd extends HttpServlet {public UserAdd() {super();}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {req.setCharacterEncoding("UTF-8");String name=req.getParameter("name");int age=Integer.parseInt(req.getParameter("age"));List<User> users=(List<User>)req.getSession().getServletContext().getAttribute("storeUsers");if(users==null){users=new ArrayList<User>();}User u=new User(name,age);users.add(u);req.getSession().getServletContext().setAttribute("storeUsers", users);resp.sendRedirect("user_list.do");}}
user_list.do
package com.yan.mvc.servlet;import java.io.IOException;import java.util.List;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 com.yan.mvc.model.User;public class UserList extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public UserList() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doPost(request, response);}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List<User>users=(List<User>)request.getSession().getServletContext().getAttribute("storeUsers");request.setAttribute("users", users);request.getRequestDispatcher("/WEB-INF/user/user_list.jsp").forward(request, response);}}
user_list.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%> <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><!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><style type="text/css">table{border-bottom:1px solid #000;border-right:1px solid #000;}table td{border-top:1px solid #000;border-left:1px solid #000;padding:5px;}</style></head><body><a href="register.do" >添加用户</a><table align="center" width="200" cellspacing="0"  cellpadding="0"><tr><td>用户名</td><td>年龄</td></tr><c:if test="${empty users }"><tr><td colspan="2">没有用户信息</td></tr></c:if><c:if test="${not empty users}"><c:forEach var="user" items="${users}"><tr><td>${user.name}</td><td><c:choose> <c:when test="${user.age gt 17 }">${user.age }</c:when><c:otherwise>未成年</c:otherwise></c:choose></td></tr></c:forEach></c:if></table></body>

----------------------------------------------------------------------------------------------------
可以发现这样虽然实现目的，将控制与视图显示分离开来，但明显一个jsp就有一个servlet，太多了，我们可以将它们进行合并成一个，可以使用传参的方式
user.do
package com.yan.mvc.servlet;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.annotation.WebServlet;import javax.jws.WebService;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yan.mvc.model.User;@WebServlet("/user.do")public class UserServlet extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public UserServlet() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doPost(request,response);}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");//动态获取访问的是哪个操作                String method=request.getParameter("method");if("add".equals(method)){add(request,response);}else if("list".equals(method)){list(request,response);}else if("register".equals(method)){register(request,response);}}protected void add(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String name=req.getParameter("name");int age=Integer.parseInt(req.getParameter("age"));List<User> users=(List<User>)req.getSession().getServletContext().getAttribute("storeUsers");if(users==null){users=new ArrayList<User>();}User u=new User(name,age);users.add(u);req.getSession().getServletContext().setAttribute("storeUsers", users);resp.sendRedirect("user.do?method=list");}protected void list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List<User>users=(List<User>)request.getSession().getServletContext().getAttribute("storeUsers");request.setAttribute("users", users);request.getRequestDispatcher("/WEB-INF/user/user_list.jsp").forward(request, response);}protected void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getRequestDispatcher("/WEB-INF/user/register.jsp").forward(request, response);}}

<%@ 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><form action="user.do?method=add" method="post"><table align="center" width="500" border="1"><tr><td>用户名称：</td><td><input type="text" name="name" value=""/></td></tr><tr><td>用户年龄：</td><td><input type="text" name="age" value=""/></td></tr><tr><td colspan="2"><input type="submit" value="添加用户"></td></tr></table></form></body></html>

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%> <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><!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><style type="text/css">table{border-bottom:1px solid #000;border-right:1px solid #000;}table td{border-top:1px solid #000;border-left:1px solid #000;padding:5px;}</style></head><body><a href="user.do?method=register" >添加用户</a><table align="center" width="200" cellspacing="0"  cellpadding="0"><tr><td>用户名</td><td>年龄</td></tr><c:if test="${empty users }"><tr><td colspan="2">没有用户信息</td></tr></c:if><c:if test="${not empty users}"><c:forEach var="user" items="${users}"><tr><td>${user.name}</td><td><c:choose> <c:when test="${user.age gt 17 }">${user.age }</c:when><c:otherwise>未成年</c:otherwise></c:choose></td></tr></c:forEach></c:if></table></body>

----------------------------------------------------------------------------------------------------
上面还有不足的地方，那就是如果操作很多，要写过多的if-else语句，怎么修改？第一时间想到了反射，根据参数自动选择要执行的方法
package com.yan.mvc.servlet;import java.io.IOException;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.List;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 com.yan.mvc.model.User;@WebServlet("/user.do")public class UserServlet extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public UserServlet() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doPost(request,response);}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");String method=request.getParameter("method");try {Method m=this.getClass().getMethod(method,HttpServletRequest.class,HttpServletResponse.class);m.invoke(this, request,response);} catch (NoSuchMethodException e) {e.printStackTrace();} catch (SecurityException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (IllegalArgumentException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}}@SuppressWarnings("unchecked")public void add(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String name=req.getParameter("name");int age=Integer.parseInt(req.getParameter("age"));List<User> users=(List<User>)req.getSession().getServletContext().getAttribute("storeUsers");if(users==null){users=new ArrayList<User>();}User u=new User(name,age);users.add(u);req.getSession().getServletContext().setAttribute("storeUsers", users);resp.sendRedirect("user.do?method=list");}@SuppressWarnings("unchecked")public void list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List<User>users=(List<User>)request.getSession().getServletContext().getAttribute("storeUsers");request.setAttribute("users", users);request.getRequestDispatcher("/WEB-INF/user/user_list.jsp").forward(request, response);}public void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getRequestDispatcher("/WEB-INF/user/register.jsp").forward(request, response);}}

可以发现现在增加方法，不用再去修改doPost()，如果用的是if-else则要不断增加else if语句。（体验反射神奇之处，不用修改，根据参数去执行某个方法，死的东西活过来了）
其实反射的那部分代码是通用的，更好的改进方法是提取出来，创建一个BaseServlet，让UserServlet去继承它。

package com.yan.mvc.servlet;import java.io.IOException;import java.lang.reflect.InvocationTargetException;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;public class BaseServlet extends HttpServlet {@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");String method=request.getParameter("method");try {Method m=this.getClass().getMethod(method,HttpServletRequest.class,HttpServletResponse.class);m.invoke(this, request,response);} catch (NoSuchMethodException e) {e.printStackTrace();} catch (SecurityException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (IllegalArgumentException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}}}

package com.yan.mvc.servlet;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yan.mvc.model.User;@WebServlet("/user.do")public class UserServlet extends BaseServlet {private static final long serialVersionUID = 1L;         @SuppressWarnings("unchecked")public void add(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String name=req.getParameter("name");int age=Integer.parseInt(req.getParameter("age"));List<User> users=(List<User>)req.getSession().getServletContext().getAttribute("storeUsers");if(users==null){users=new ArrayList<User>();}User u=new User(name,age);users.add(u);req.getSession().getServletContext().setAttribute("storeUsers", users);resp.sendRedirect("user.do?method=list");}@SuppressWarnings("unchecked")public void list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List<User>users=(List<User>)request.getSession().getServletContext().getAttribute("storeUsers");request.setAttribute("users", users);request.getRequestDispatcher("/WEB-INF/user/user_list.jsp").forward(request, response);}public void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getRequestDispatcher("/WEB-INF/user/register.jsp").forward(request, response);}}

这样一来真正通用，不仅是UserServlet，以后有什么AddressServlet、MessageServlet等等都可以去继承它，在这些servlet中我们只顾写需要的业务方法就好了（就好像UserServlet只要写add()、list()、register()这些方法，神奇！！！），
进一步把页面跳转代码给提取出来
package com.yan.mvc.servlet;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yan.mvc.model.User;@WebServlet("/user.do")public class UserServlet extends BaseServlet {private static final long serialVersionUID = 1L;         @SuppressWarnings("unchecked")public String add(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String name=req.getParameter("name");int age=Integer.parseInt(req.getParameter("age"));List<User> users=(List<User>)req.getSession().getServletContext().getAttribute("storeUsers");if(users==null){users=new ArrayList<User>();}User u=new User(name,age);users.add(u);req.getSession().getServletContext().setAttribute("storeUsers", users);return "redirect:user.do?method=list";//resp.sendRedirect("user.do?method=list");}@SuppressWarnings("unchecked")public String list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List<User>users=(List<User>)request.getSession().getServletContext().getAttribute("storeUsers");request.setAttribute("users", users);return "user/user_list.jsp";//request.getRequestDispatcher("/WEB-INF/user/user_list.jsp").forward(request, response);}public String register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//request.getRequestDispatcher("/WEB-INF/user/register.jsp").forward(request, response);return "user/register.jsp";}}

package com.yan.mvc.servlet;import java.io.IOException;import java.lang.reflect.InvocationTargetException;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;public class BaseServlet extends HttpServlet {@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");String method=request.getParameter("method");try {Method m=this.getClass().getMethod(method,HttpServletRequest.class,HttpServletResponse.class);//获取要跳转到的页面
                        String rel=(String)m.invoke(this, request,response);String redirStr="redirect:";
//判断客户端跳转还是服务器端跳转if(rel.startsWith(redirStr)){response.sendRedirect(rel.substring(redirStr.length()));}else{request.getRequestDispatcher("/WEB-INF/"+rel).forward(request, response);}} catch (NoSuchMethodException e) {e.printStackTrace();} catch (SecurityException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (IllegalArgumentException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}}}

                                             
        0        0           
	
				
		









 二维数组元素的排序 c
    		二维数组元素的排序 c



原创粉丝点击



		

热门IT博客


企查查怎么看数据企查查怎么看数据




破解软件网站大全破解软件网站大全




网络合同




js清空input file内容




全国社保统筹 知乎




unity3d2017可以用java




安广网络客服电话淮南




伍迪艾伦 知乎




淘宝小铺名称能改吗




专业跑步软件




重庆美皇公司知乎




淘宝不能朋友代付




原生js设置data属性




js查找节点的方法




windows 系统错误




路由器mac地址过滤功能




unity3d圣典中文手册




js怎么写乘法表




电商可变数据印刷




备案是每一个域名



		

热门问题
    老师的惩罚
    人脸识别
    我在镇武司摸鱼那些年
    重生之率土为王
    我在大康的咸鱼生活
    盘龙之生命进化
    天生仙种
    凡人之先天五行
    春回大明朝
    姑娘不必设防，我是瞎子
    学习心得体会
    个人心得体会200字
    党课学习体会
    心得体会怎么写
    白皮书心得体会
    家长会心得体会
    榜样3心得体会
    榜样4心得体会
    党课心得体会
    心得体会范文
    军训心得体会800
    体会是什么意思
    体会内衣质量怎么样
    体会内衣好吗
    培训心得体会怎么写
    减肥心得体会
    练字心得体会
    钳工实训体会
    工作心得体会
    销售心得体会总结
    会计培训体会
    隆鼻假体会下滑吗
    开网店心得体会
    心理培训体会
    敬老院心得体会
    计算机学习体会
    化验室心得体会
    听课体会怎么写
    学习班心得体会
    普法学习体会
    工作学习体会
    学习的心得体会
    心得报告
    师德师风心得体会
    党课学习心得体会
    金融行业心得体会
    正风肃纪心得体会
    社会实践心得体会
    坚定信念心得体会
    警示教育心得体会
    研学旅行心得体会


	










程序博客网，程序员的互联网技术博客家园。csdn论坛精品 msdn技术资料都在这里