web应用之监听器

package com.log.service;

import java.util.Enumeration;

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

import com.util.UtilPrint;

/**
 * 对应慕课网 3-1，http://www.imooc.com/video/5658，
 *  ServletContextListener的主要用途：
 * 1 定时器
 * 2 获取全局属性对象(设置全局属性对象)
 * 3 获取web.xml中的初始化参数
 * @author Wei
 * @time 2016年10月4日 下午8:38:37
 */
public class WylContextListener implements ServletContextListener {

	public WylContextListener() {
		System.out.println("com.log.service.WylContextListener()实例化,");
	}

	@Override
	public void contextInitialized(ServletContextEvent sce) {
		System.out.println("com.log.service.WylContextListener.contextInitialized()...,");
		ServletContext sc = sce.getServletContext();
		/**
		 * 设置全局变量，然后再整个应用的生命周期里都可以获取到
		 */
		sc.setAttribute("theGlobalPara", "我是全局的属性对象，");
		Enumeration<String> initparaNames = sc.getInitParameterNames();
		if (initparaNames.hasMoreElements()) {
			String name = initparaNames.nextElement();
			/**
			 * 获取web.xml中的初始化参数，
			 * <context-param>
			 * 		<param-name>ctxName</param-name>
			 * 		<param-value>我是ctx的值</param-value>
			 * </context-param>
			 */
			String initValue = sc.getInitParameter(name);
			UtilPrint.printWithSeparatorAndClass("------name:" + name + ",initValue:" + initValue,
					WylContextListener.class);
		} else {
			UtilPrint.printWithSeparatorAndClass("com.log.service.WylContextListener.contextInitialized()...,没有获取到初始化参数", WylContextListener.class);
		}
	}
	@Override
	public void contextDestroyed(ServletContextEvent sce) {
		// TODO Auto-generated method stub
		System.out.println("com.log.service.WylContextListener.contextDestroyed()...,");
	}

}

　　web.xml:

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
     id="WebApp_ID" version="2.5">

     <!-- 配置 Struts2 的 Filter -->
     <welcome-file-list>

         <!-- <welcome-file>index.jsp</welcome-file> 欢迎页改为MyTag.jsp -->
         <welcome-file>MyTag.jsp</welcome-file>
     </welcome-file-list>

     <listener>
         <listener-class>com.log.service.WylSessionAttrbuteLister</listener-class>
     </listener>

     <listener>
         <listener-class>com.log.service.WylSessionListener</listener-class>
     </listener>
     <!-- ServletRequestListener -->
     <listener>
         <listener-class>com.log.service.WylServletRequestListener</listener-class>
     </listener>

     <listener>
         <listener-class>com.log.service.WylContextListener</listener-class>
     </listener>

     <servlet>
         <servlet-name>freemarker</servlet-name>
         <servlet-class>freemarker.ext.servlet.FreemarkerServlet</servlet-class>
         <!--下面的配置freemarke的ftl文件的位置 -->
         <init-param>
             <param-name>TemplatePath</param-name>
             <param-value>/</param-value>
         </init-param>
         <!-- 是否和服务器（tommcat)一起启动。0为不。1为是 -->
         <load-on-startup>1</load-on-startup>
     </servlet>

     <servlet-mapping>
         <servlet-name>freemarker</servlet-name>
         <url-pattern>*.ftl</url-pattern>
     </servlet-mapping>

     <servlet>
         <!-- define a JspSupportServlet Object -->
         <servlet-name>JspSupportServlet</servlet-name>
         <servlet-class>org.apache.struts2.views.JspSupportServlet</servlet-class>
         <!-- setting JspSupportServlet auto start -->
         <load-on-startup>1</load-on-startup>
     </servlet>

     <!-- <filter> <filter-name>struts2</filter-name> <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
         </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>/*</url-pattern>
         </filter-mapping> -->
     <filter>
         <filter-name>struts2</filter-name>
         <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
     </filter>

     <filter-mapping>
         <filter-name>struts2</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <!-- 我的自定义过滤器 -->

     <filter>
         <filter-name>wylFiler3</filter-name>
         <filter-class>com.test.javaAPI.servlet.MyFilter3</filter-class>
     </filter>

     <filter-mapping>
         <filter-name>wylFiler3</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <filter>
         <filter-name>wylFiler4</filter-name>
         <filter-class>com.test.javaAPI.servlet.MyFilterXX</filter-class>
     </filter>

     <filter-mapping>
         <filter-name>wylFiler4</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <filter>
         <filter-name>wylFiler1</filter-name>
         <filter-class>com.test.javaAPI.servlet.MyFilter1</filter-class>
     </filter>

     <filter-mapping>
         <filter-name>wylFiler1</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <filter>
         <filter-name>wylFiler2</filter-name>
         <filter-class>com.test.javaAPI.servlet.MyFilter2</filter-class>
     </filter>

     <filter-mapping>
         <filter-name>wylFiler2</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <!-- 测试servlet用的，20161004 -->
     <servlet>
         <servlet-name>testMy</servlet-name>
         <servlet-class>com.test.javaAPI.servlet.MyServlet</servlet-class>

     </servlet>

     <servlet-mapping>
         <servlet-name>testMy</servlet-name>
         <url-pattern>*.xxx</url-pattern>
     </servlet-mapping>

     <!-- 测试servlet用的，20161004 -->
     <servlet>
         <servlet-name>testMy2</servlet-name>
         <servlet-class>com.test.javaAPI.servlet.MyServlet2</servlet-class>
         <!-- 设置 web容器已启动就实例化这个servlet，servlet一旦实例化就会调用初始化方法init(),而且生命周期里只会实例化一次 -->
         <load-on-startup>1</load-on-startup>
     </servlet>

     <servlet-mapping>
         <servlet-name>testMy2</servlet-name>
         <url-pattern>*.yyy</url-pattern>
     </servlet-mapping>
     <!-- 可以通过通过监听器来获取到，当然了，需要实现ServletContextListener接口 ，
     见：com.log.service.WylContextListener-->
     <context-param>
         <param-name>ctxName</param-name>
         <param-value>我是ctx的值</param-value>
     </context-param>

 </web-app>

如下图，已经获取到web.xml中的<context-param>标签中设置的值了，