Listener-监听器处理路径问题

为了达到下面的目的

<% application.setAttribute("app",request.getContextPath() ); %>
<frame src="${app}/backend/_top.jsp" noresize="noresize"/>

可以做如下操作

package listener;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * ServletContext域对象的生死监听器
 */
public class MyServletContextListener implements ServletContextListener {

    /**
     * ServletContext域对象创建时立即执行
     */
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        ServletContext context = sce.getServletContext();
        //1.获取当前Web应用的虚拟路径 
        String contextPath = context.getContextPath();
        //2.将虚拟路径存入ServletContext域中
        context.setAttribute("app", contextPath);
        System.out.println("app 初始化完成");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        
    }
    
}

web.xml

 <listener>
    <listener-class>listener.MyServletContextListener</listener-class>
  </listener>