一个简单的mvc实现

  从一本书上看到一个mvc的简单实现，有点像struts2，大家分享一下
  1、核心一个FrontController拦截所有请求，web.xml如下： 

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" 
	xmlns="http://java.sun.com/xml/ns/j2ee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
	http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>FrontController</servlet-name>
    <servlet-class>am.core.FrontController</servlet-class>
    <init-param>
    	<param-name>config</param-name>
    	<param-value>/WEB-INF/classes/am-config.xml</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>FrontController</servlet-name>
    <url-pattern>*.action</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
  </welcome-file-list>
</web-app>

 
 
FrontController：

package am.core; 

import java.io.IOException; 
import java.util.Map; 

import javax.servlet.RequestDispatcher; 
import javax.servlet.ServletContext; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import org.apache.commons.logging.Log; 
import org.apache.commons.logging.LogFactory; 

import am.common.Const; 
import am.util.ConfigXMLParser; 

public class FrontController extends HttpServlet { 
private static final Log log=LogFactory.getLog(ConfigXMLParser.class); 
/** 
* Initialization of the servlet. <br> 
* 
* @throws ServletException if an error occure 
*/ 
public void init() throws ServletException { 
ServletContext context=this.getServletContext(); 
String config_file=this.getServletConfig().getInitParameter("config"); 
String dispatcher_name=this.getServletConfig().getInitParameter("dispatcher"); 
if(config_file==null||config_file.equals("")) 
config_file="/WEB-INF/classes/am-config.xml"; 
if(dispatcher_name==null||dispatcher_name.equals("")) 
dispatcher_name=Const.DEFAULT_DISPATCHER; 
try{ 
Map<String,ActionModel> resources=ConfigXMLParser.newInstance().parse(config_file,context); 
System.out.println(resources); 
context.setAttribute(Const.ACTIONS_ATTR, resources); 
log.info("初始化配置文件成功"); 
}catch(Exception e){ 
log.error("初始化配置文件失败"); 
e.printStackTrace(); 
} 
try{ 
Class c=Class.forName(dispatcher_name); 
Dispatcher dispatcher=(Dispatcher)c.newInstance(); 
context.setAttribute(Const.DISPATCHER_ATTR, dispatcher); 
log.info("初始化Dispatcher成功"); 
}catch(Exception e){ 
log.error("初始化Dispatcher失败"); 
e.printStackTrace(); 
} 
} 

    /** 
* The doGet method of the servlet. <br> 
* 
* This method is called when a form has its tag value method equals to get. 
* 
* @param request the request send by the client to the server 
* @param response the response send by the server to the client 
* @throws ServletException if an error occurred 
* @throws IOException if an error occurred 
*/ 
public void doGet(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException { 
        this.process(request, response); 

} 

/** 
* The doPost method of the servlet. <br> 
* 
* This method is called when a form has its tag value method equals to post. 
* 
* @param request the request send by the client to the server 
* @param response the response send by the server to the client 
* @throws ServletException if an error occurred 
* @throws IOException if an error occurred 
*/ 
public void doPost(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException { 
this.process(request, response); 

} 
protected void process(HttpServletRequest request, 
HttpServletResponse response)throws ServletException,IOException{ 
ServletContext context=this.getServletContext(); 
String reqURL=request.getRequestURL().toString(); 
int i=reqURL.lastIndexOf("."); 
String contextPath=request.getContextPath(); 
int j=reqURL.indexOf(contextPath); 
String path=reqURL.substring(contextPath.length()+j,i); 
request.setAttribute(Const.REQUEST_ATTR, path); 
Dispatcher dispatcher=(Dispatcher)context.getAttribute(Const.DISPATCHER_ATTR); 
String nextPage=dispatcher.getNextUrl(request, response, context); 
RequestDispatcher forwarder=request.getRequestDispatcher("/"+nextPage); 
forwarder.forward(request,response); 
} 

} 

 
am-config.xml为配置文件，结构如下：

<?xml version="1.0" encoding="UTF-8"?>
<actions>
<action path="/login" class="am.action.LoginAction">
<forward name="success" url="hello.jsp"/> 
<forward name="error" url="login.jsp"/> 
</action>
</actions>

 
FrontController拦截所有请求，根据请求URL解析出path，根据path由Dispatcher执行具体action，返回nextpage。
ActionDispatcher如下： 
 

package am.core; 
import java.util.Map; 
import javax.servlet.ServletContext; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import org.apache.commons.logging.Log; 
import org.apache.commons.logging.LogFactory; 
import am.common.Const; 

public class ActionDispatcher implements Dispatcher { 
private ServletContext context; 
private static final Log log=LogFactory.getLog(ActionDispatcher.class); 
public String getNextUrl(HttpServletRequest request, 
HttpServletResponse response, ServletContext context) { 
setServletContext(context); 
Map<String,ActionModel> actions= 
(Map<String,ActionModel>)context.getAttribute(Const.ACTIONS_ATTR); 
String reqPath=(String)request.getAttribute(Const.REQUEST_ATTR); 
ActionModel actionModel=actions.get(reqPath); 
String forward_name=""; 
ActionForward actionForward; 
try{ 
Class c=Class.forName(actionModel.getClassName()); 
Action action=(Action)c.newInstance(); 
if(ValuesSetter.setValues(request, action)){ 
forward_name=action.execute(request, response, context); 
}else{ 
forward_name=Action.ERROR; 
} 
}catch(Exception e){ 
log.error("can not find action"+actionModel.getClassName()); 
} 
actionForward=actionModel.getForwards().get(forward_name); 
if(actionForward==null){ 
log.error("can not find page for forward "+forward_name); 
return null; 
}else{ 
return actionForward.getViewUrl(); 
} 
     } 

public void setServletContext(ServletContext context) { 
// TODO Auto-generated method stub 
this.context = context; 
} 
} 

 
实现原理和struts差不多，有助于我们理解struts，具体代码可见附件。