strust2页面分发机制模拟

模拟步骤：

一、 监听器
1、 准备一个map
2、 把所有的action的key,value放入到map中
3、 把map放入到application域中
二、 过滤器
1、 获取application域中的map
2、 解析url
3、 根据解析的url从map中把value提取出来
4、 根据java的反射机制动态调用action
5、 根据action返回的方法跳转到相应的页面
三、执行action 的execute方法，该方法返回一个字符串

（1）监听器加载mapimport java.util.HashMap;import java.util.Map;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;public class ServletListener implements ServletContextListener {//tomcat关闭的时候被调用@Overridepublic void contextDestroyed(ServletContextEvent arg0) {arg0.getServletContext().removeAttribute("maping");System.out.println("监听器被摧毁！");}//tomcat启动的时候被加载@Overridepublic void contextInitialized(ServletContextEvent arg0) {Map<String,String> map  = new HashMap<String,String>();map.put("Myaction", "com.itheima.structstest.Myaction");arg0.getServletContext().setAttribute("maping", map);System.out.println("监听器被初始化了----------------------------------------------！");}}（2）编写Action类返回要调用的结果public class Myaction {public String execute() {return "index.jsp";//返回一个需要跳转的页面}}（3）编写过滤器完成对后缀为.action的请求过滤public class FilterControl implements Filter {private FilterConfig myConfig;@Overridepublic void destroy() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest arg0, ServletResponse arg1,FilterChain arg2) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest)arg0;HttpServletResponse response = (HttpServletResponse)arg1;//获取监听器中存储的mapMap<String,String> map =(Map<String,String>)myConfig.getServletContext().getAttribute("maping");//获取请求的URI中具体的请求ActionString key = ActionUtil(request.getRequestURI());//获取对应action在map中的类String obj = (String)map.get(key);//一下功能室通过反射原理调用相应的方法，得到需要的转发页面，然后进行转发try {Class clazz = Class.forName(obj);System.out.println(clazz);Method me = clazz.getMethod("execute", null);String exem = (String)me.invoke(clazz.newInstance(), null);request.getRequestDispatcher(exem).forward(request, response);} catch (Exception e) {e.printStackTrace();}}public String  ActionUtil(String url) {String[] str = url.split("/");String lastStr = str[str.length-1];return  lastStr.substring(0,lastStr.indexOf("."));}@Overridepublic void init(FilterConfig arg0) throws ServletException {// TODO Auto-generated method stubthis.myConfig = arg0;}}（4）web.xml中的配置<listener>  <listener-class>com.itheima.structstest.ServletListener</listener-class>  </listener>  <filter>  <filter-name>FilterControl</filter-name>  <filter-class>com.itheima.structstest.FilterControl</filter-class>  </filter>  <filter-mapping>  <filter-name>FilterControl</filter-name>  <url-pattern>*.action</url-pattern>  </filter-mapping>（5）请求测试http://localhost:8080/test/Myaction.action   //请求Myaction的资源