设计模式MVC

设计模式之MVC基于Web 主讲：Hesey

提纲 What and Why 优缺点实例分析举一反三

What is MVC? MVC模式（Model-View-Controller）是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）和控制器（Controller）。目的：动态的程序设计简化后续修改和扩展复用代码专一化（模块、人员）

视图界面设计人员进行图形界面设计展示数据（不仅仅是显示）无业务逻辑

控制器负责转发请求，对请求进行处理不同层面间的组织作用控制应用程序的流程处理事件并作出响应

模型包含程序应有的功能（实现算法等） Bean/Service/DAO etc. 封装数据与逻辑直接访问数据（DB）不依赖“视图”和“控制器” 刷新机制

原始时代(JSP or Servlet) Password.htm <HTML> <BODY> <form action="PasswordGen.jsp" method="POST"> <H3>Welcome to the Password Generator</H3> First Name: <input type="text" name="firstName"><br> Last Name: <input type="text" name="lastName"><br> <p> <input type="submit" value="Generate Password"> </form> </BODY> </HTML>

原始时代(JSP or Servlet) PasswordGen.jsp <html> <body> <% String firstName = request.getParameter("firstName"); String lastName = request. getParameter("lastName"); String password; if( (firstName.length()>=2) && (lastName.length()>=2)) password = lastName.substring(0,2)+firstName.substring(0,2); else password = "NoGo"; %> <h1> Password Generated! </h1> Your super secret password is <%= password %>. <br><a href="Password.htm">To generate another password.</a> </body> </html>

原始时代(JSP or Servlet) PasswordGen.jsp <html> <body> <% String firstName = request.getParameter("firstName"); String lastName = request. getParameter("lastName"); String password; if( (firstName.length()>=2) && (lastName.length()>=2)) password = lastName.substring(0,2)+firstName.substring(0,2); else password = "NoGo"; %> <h1> Password Generated! </h1> Your super secret password is <%= password %>. <br><a href="Password.htm">To generate another password.</a> </body> </html> 看着都费劲，别说修改了╮(╯_╰)╭

缺点职责多元 HTML代码和Java代码混杂（好眼花⊙﹏⊙）修改逻辑or 修改呈现？代码复用？（审核身份、日志记录）团队开发困难

优点解耦职责单一分工明确（模块、人员）代码复用测试方便对比职责多元 HTML代码和Java代码混杂（好眼花）修改逻辑 or 修改呈现？增加服务？代码复用？（审核身份、日志记录）团队开发困难

缺点比较抽象没有明确的定义，难以完全理解需要精心计划与设计，花费可观更多文件，更多代码，增加了复杂度这么复杂，为什么还要用？弥补：框架

Servlet and JSP Password.htm <HTML> <BODY> <form action="/webapp/passwordservlet" method="POST"> <H3>Welcome to the Password Generator</H3> First Name: <input type="text" name="firstName"><br> Last Name: <input type="text" name="lastName"><br> <p> <input type="submit" value="Generate Password"> </form> </BODY> </HTML>

Servlet and JSP passwordServlet.java public void doPost(HttpServletRequest request, HttpServletResponse response) throws Exception { GenBeangb = new GenBean(); gb.setFirstName(request.getParameter("firstName")); gb.setLastName(request.getParameter("lastName")); gb.generate(); request.setAttribute("gen", gb); RequestDispatcherrd = getServletContext().getRequestDispatcher("/PasswordGen.jsp"); rd.forward(request, response); }

Servlet and JSP GenBean.java public class GenBean { private String firstName; private String lastName; private String password = "NoGo"; public String getFirstName(){ return firstName; } public void setFirstName(String fn){ firstName = fn;} public String getLastName(){ return lastName; } public void setLastName(String ln){ lastName = ln; } public String getPassword(){return password;} public String generate() { if( (firstName.length() >= 2) && (lastName.length() >= 2)) password = lastName.substring(0,2) + firstName.substring(0,2); return password; } }

Servlet and JSP PasswordGen.jsp <html> <body> <jsp:useBean id = "gen" class = “genpackage.GenBean" scope="request"/> <h1> Password Generated! </h1> Your super secret password is <jsp:getProperty name="gen" property="password"/> <br><a href="Password.htm">To generate another password.</a> </body> </html> 清晰了很多吧o(≧v≦)o~~

体现分发的Servlet控制器 verify.java public void doPost(HttpServletRequest request, HttpServletResponse response) throws Exception { String username = request.getParameter(“username")); String password = request.getParameter(“password")); boolean valid = new Security().verify(username, password); RequestDispatcherrd= null; if(valid) { rd= getServletContext().getRequestDispatcher("/valid.jsp"); } else { rd= getServletContext().getRequestDispatcher("/invalid.jsp"); } rd.forward(request, response); }

现在呈现和逻辑被分开了，真好呀 Servlet 1 JSP 1 Servlet 2 JSP 2 Servlet 3 JSP 3 有没有改进的余地？

如果把Servlet组合起来？ Controller JSP 1 Model 1 JSP 2 Model 2 JSP 3 Model 3 关系是不是简单了许多？

Model Action 1 Action 2 Action 3 Bean DAO Service Struts 2 XML配置 Controller Struts 2 Dispatcher 浏览器 Web容器 View JSP 1 JSP 2 DataBase

web.xml <filter> <filter-name>struts2</filter-name> <filter-class> org.apache.struts2.dispatcher.FilterDispatcher </filter-class> </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>

Struts.xml <struts> <package name=“default” extends=“struts-default”> <action name=“hello” class=“HelloWorld”> <result name=“SUCCESS”> /HelloWorld.jsp </result> </action> </package> </struts>

HelloWorld.java(POJO) public class HelloWorld { private String message; public String execute() Exception { message = “Hello,world”; message += “The time is:”; message += System.currentTimeMillis(); return “SUCCESS”; } public void setMessage(String message){this.message = message; } public String getMessage() { return message; }}

HelloWorld.jsp <%@ taglib prefix="s" uri="/struts-tags" %><html><head><title>Hello World!</title></head><body><h2><s:property value="message" /></h2></body></html>

举一反三思考模式思想，套用模式不如不用模式解耦单一职责原则（SRP）测试

设计模式MVC

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