一个简单MVC模式的实现

简单MVC模式的实现主要由3部分组成,用于初始化的ConfigListener,控制器 Controller和配置文件 mvc_config.xml

1 监听器ConfigListener
主要用于在初始化ServletContext时读入配置文件，并把路径和转发信息储存在attribute中。代码如下：

  public class ConfigListener implements ServletContextListener {
     public void contextInitialized(ServletContextEvent event) {
		// TODO Auto-generated method stub
		SAXReader reader = new SAXReader();
        try {
			Document document = reader.read(ConfigListener.class.getClassLoader().getResourceAsStream("mvc_config.xml"));
			Element root=document.getRootElement();
                        //将读出的信息保存在map中
			Map config=new HashMap();
			for(Iterator it=root.elementIterator("path");it.hasNext();){
				Element e=(Element)it.next();
				config.put(e.attributeValue("name"), e.elementText("forward"));
			}
                        //将map保存在context中
			event.getServletContext().setAttribute("config", config);
			/*System.out.println(paths.size());
			  for(int i=0; i<paths.size(); i++){
				Element e=(Element)paths.get(i);
				System.out.println(e.attributeValue("name"));
				System.out.println(e.elementText("goto"));
			}*/
		} catch (DocumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
  }

2 控制器 Controller

  public class Controller extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		doPost(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		PrintWriter out=resp.getWriter();
		Map parameters=req.getParameterMap();
                //...将参数进行验证或封装
		String path=req.getServletPath().replace(".do", "");
		System.out.println(path);
		Map config=(Map)getServletContext().getAttribute("config");
		//out.println(config);
		String forward=(String)config.get(path);
		//out.println(forward);
		RequestDispatcher dispatcher=req.getRequestDispatcher(forward);
		dispatcher.forward(req, resp);
	}
}

在web.xml中配置Controller的url-pattern为*.do(也可以为其它)

 <servlet-mapping>
  	<servlet-name>Controller</servlet-name>
  	<url-pattern>*.do</url-pattern>
  </servlet-mapping>

3 配置文件mvc_config.xml

  <?xml version="1.0" encoding="UTF-8"?>
<paths>
   <!-- must start with / and no extension like .do or others -->
   <path name="/reg">
      <forward>/register</forward>
    </path>
    <path name="/login">
      <forward>/pages/login.jsp</forward>
    </path>
    <path name="/welcome">
	<forward>/</forward>
    </path>
</paths>

访问 http://xxx/webapp/reg.do， 转发到/register
访问 http://xxx/webapp/login， 转发到/pages/login.jsp
访问 http://xxx/webapp/welcome， 转发到/