Servlet是一种服务器端的编程语言，是J2EE中比较关键的组成部分，Servlet技术的推出，扩展了Java语言在服务器端开发的功能，巩固了Java语言在服务器端开发中的地位，而且现在使用非常广泛的JSP技术也是基于Servlet的原理.
JSP+JavaBeans+Servlet成为实现MVC模式的一种有效的选择。
如果我们要实现一个对用户的增删改查，，并且要求符合对扩展开发，对修改关闭的原则，该怎么做呢？
首先，这是我们的类图以及类与类之间调用的时序图。
根据UML图来实现代码：
TestServlet类
package com.bjpowernode.servlet;import java.io.IOException;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class TestServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String requestURI = request.getRequestURI();System.out.println("requestURI=" + requestURI);String path = requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf("."));System.out.println("path = " +path);String username = request.getParameter("username");Action action = null;if("/servlet/delUser".equals(path)){action = new DelUserAction();}else if("/servlet/addUser".equals(path)){action = new AddUserAction();}else if("/servlet/modifyUser".equals(path)){action = new ModifyAction();}else if("/servlet/queryUser".equals(path)){action = new QueryUserAction();}else{throw new RuntimeException("请求失败");}String forward ="";try {forward= action.execute(request, response);} catch (Exception e) {e.printStackTrace();}request.getRequestDispatcher(forward).forward(request, response);}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request,response);}}
抽象接口Action
package com.bjpowernode.servlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public interface Action {public String execute(HttpServletRequest request, HttpServletResponse response)throws Exception;}
添加类，这里就只写添加类了，其他类一样
package com.bjpowernode.servlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class AddUserAction implements Action {public String execute(HttpServletRequest request,HttpServletResponse response) throws Exception {String username = request.getParameter("username");//int age = Integer.parseInt(request.getParameter("username"));//String sex = request.getParameter("sex");//调用业务逻辑UserManager userManager = new UserManager();userManager.add(username);return "/add_success.jsp";}}
Web.xml配置
<welcome-file-list><welcome-file>index.jsp</welcome-file> </welcome-file-list><servlet> <servlet-name>TestServlet</servlet-name> <servlet-class>com.bjpowernode.servlet.TestServlet</servlet-class> </servlet> <servlet-mapping><servlet-name>TestServlet</servlet-name><!–<url-pattern>/servlet/TestServlet</url-pattern>–><url-pattern>*.do</url-pattern> </servlet-mapping>
这里我们发现，在testAction类中，用到了大量的if和else，而当我们需要扩展一个上传类的时候，就需要修改if/else，所以，这就不符合对扩展开发，对修改关闭原则，所以，我们需要把这部分提取出来，配置到配置文件里，用反射进行配置。
我们需要先配置配置文件
<action-config><action path ="/servlet/delUser" type = "com.bjpowernode.servlet.DelUserAction"><forward name = "success">del_success.jsp</forward><forward name = "error">del_error.jsp</forward></action><action path ="/servlet/addUser" type = "com.bjpowernode.servlet.AddUserAction"><forward name = "success">add_success.jsp</forward><forward name = "error">add_error.jsp</forward></action><action path ="/servlet/modifyUser" type = "com.bjpowernode.servlet.ModifyAction"><forward name = "success">modify_success.jsp</forward><forward name = "error">modify_error.jsp</forward></action><action path ="/servlet/queryUser" type = "com.bjpowernode.servlet.QueryUserAction"><forward name = "success">query_success.jsp</forward><forward name = "error">query_error.jsp</forward></action></action-config>一路走来，我们无法猜测将是迎接什么样的风景，
