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:

  1 <?xml version="1.0" encoding="UTF-8"?>
  2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  3     xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
  4     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
  5     id="WebApp_ID" version="2.5">
  6 
  7 
  8     <!-- 配置 Struts2 的 Filter -->
  9     <welcome-file-list>
 10 
 11         <!-- <welcome-file>index.jsp</welcome-file> 欢迎页改为MyTag.jsp -->
 12         <welcome-file>MyTag.jsp</welcome-file>
 13     </welcome-file-list>
 14 
 15     <listener>
 16         <listener-class>com.log.service.WylSessionAttrbuteLister</listener-class>
 17     </listener>
 18 
 19     <listener>
 20         <listener-class>com.log.service.WylSessionListener</listener-class>
 21     </listener>
 22     <!-- ServletRequestListener -->
 23     <listener>
 24         <listener-class>com.log.service.WylServletRequestListener</listener-class>
 25     </listener>
 26 
 27     <listener>
 28         <listener-class>com.log.service.WylContextListener</listener-class>
 29     </listener>
 30     
 31     <servlet>
 32         <servlet-name>freemarker</servlet-name>
 33         <servlet-class>freemarker.ext.servlet.FreemarkerServlet</servlet-class>
 34         <!--下面的配置freemarke的ftl文件的位置 -->
 35         <init-param>
 36             <param-name>TemplatePath</param-name>
 37             <param-value>/</param-value>
 38         </init-param>
 39         <!-- 是否和服务器（tommcat)一起启动。0为不。1为是 -->
 40         <load-on-startup>1</load-on-startup>
 41     </servlet>
 42 
 43     <servlet-mapping>
 44         <servlet-name>freemarker</servlet-name>
 45         <url-pattern>*.ftl</url-pattern>
 46     </servlet-mapping>
 47 
 48 
 49     <servlet>
 50         <!-- define a JspSupportServlet Object -->
 51         <servlet-name>JspSupportServlet</servlet-name>
 52         <servlet-class>org.apache.struts2.views.JspSupportServlet</servlet-class>
 53         <!-- setting JspSupportServlet auto start -->
 54         <load-on-startup>1</load-on-startup>
 55     </servlet>
 56 
 57 
 58     <!-- <filter> <filter-name>struts2</filter-name> <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> 
 59         </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>/*</url-pattern> 
 60         </filter-mapping> -->
 61     <filter>
 62         <filter-name>struts2</filter-name>
 63         <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
 64     </filter>
 65 
 66     <filter-mapping>
 67         <filter-name>struts2</filter-name>
 68         <url-pattern>/*</url-pattern>
 69     </filter-mapping>
 70 
 71     <!-- 我的自定义过滤器 -->
 72 
 73 
 74     <filter>
 75         <filter-name>wylFiler3</filter-name>
 76         <filter-class>com.test.javaAPI.servlet.MyFilter3</filter-class>
 77     </filter>
 78 
 79     <filter-mapping>
 80         <filter-name>wylFiler3</filter-name>
 81         <url-pattern>/*</url-pattern>
 82     </filter-mapping>
 83 
 84     <filter>
 85         <filter-name>wylFiler4</filter-name>
 86         <filter-class>com.test.javaAPI.servlet.MyFilterXX</filter-class>
 87     </filter>
 88 
 89     <filter-mapping>
 90         <filter-name>wylFiler4</filter-name>
 91         <url-pattern>/*</url-pattern>
 92     </filter-mapping>
 93 
 94 
 95     <filter>
 96         <filter-name>wylFiler1</filter-name>
 97         <filter-class>com.test.javaAPI.servlet.MyFilter1</filter-class>
 98     </filter>
 99 
100     <filter-mapping>
101         <filter-name>wylFiler1</filter-name>
102         <url-pattern>/*</url-pattern>
103     </filter-mapping>
104 
105     <filter>
106         <filter-name>wylFiler2</filter-name>
107         <filter-class>com.test.javaAPI.servlet.MyFilter2</filter-class>
108     </filter>
109 
110     <filter-mapping>
111         <filter-name>wylFiler2</filter-name>
112         <url-pattern>/*</url-pattern>
113     </filter-mapping>
114 
115 
116     <!-- 测试servlet用的，20161004 -->
117     <servlet>
118         <servlet-name>testMy</servlet-name>
119         <servlet-class>com.test.javaAPI.servlet.MyServlet</servlet-class>
120 
121     </servlet>
122 
123     <servlet-mapping>
124         <servlet-name>testMy</servlet-name>
125         <url-pattern>*.xxx</url-pattern>
126     </servlet-mapping>
127 
128 
129     <!-- 测试servlet用的，20161004 -->
130     <servlet>
131         <servlet-name>testMy2</servlet-name>
132         <servlet-class>com.test.javaAPI.servlet.MyServlet2</servlet-class>
133         <!-- 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 -->
134         <load-on-startup>1</load-on-startup>
135     </servlet>
136 
137     <servlet-mapping>
138         <servlet-name>testMy2</servlet-name>
139         <url-pattern>*.yyy</url-pattern>
140     </servlet-mapping>
141     <!-- 可以通过通过监听器来获取到，当然了，需要实现ServletContextListener接口 ，
142     见：com.log.service.WylContextListener-->
143     <context-param>
144         <param-name>ctxName</param-name>
145         <param-value>我是ctx的值</param-value>
146     </context-param>
147 
148 </web-app>

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