Web.xml配置详解之listener

• 定义

<listener>
<listen-class>com.myapp.MyListener</listen-class>
</listener>

• 作用
  该元素用来注册一个监听器类。可以收到事件什么时候发生以及用什么作为响应的通知。事件监听程序在建立、修改和删除会话或servlet环境时得到通知。常与context-param联合使用。
• listen-class 指定监听类，该类继承ServletContextListener 包含初始化方法contextInitialized(ServletContextEvent event) 和 销毁方法contextDestoryed(ServletContextEvent event)
• 示例：初始化日志配置文件

 <!--初始化日志配置文件 -->  
 <listener>  
     <listener-class>  
         com.myapp.LogbackConfigListener  
     </listener-class>  
 </listener>  
 <context-param>  
     <param-name>logbackConfigLocation</param-name>  
     <param-value>WEB-INF/logback.xml</param-value>  
 </context-param>  

/**
 * 
 */
package com.myapp;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import org.slf4j.Logger;  
import org.slf4j.LoggerFactory;  
import ch.qos.logback.classic.LoggerContext;  
import ch.qos.logback.classic.joran.JoranConfigurator;  
import ch.qos.logback.core.joran.spi.JoranException; 
/**
 * @author louisliao
 *
 */
public class LogbackConfigListener implements ServletContextListener {

	private static final Logger logger = LoggerFactory.getLogger(LogbackConfigListener.class);  
	private static final String CONFIG_LOCATION = "logbackConfigLocation";  
	/* (non-Javadoc)
	 * @see javax.servlet.ServletContextListener#contextDestroyed(javax.servlet.ServletContextEvent)
	 */
	public void contextDestroyed(ServletContextEvent arg0) {
		// TODO Auto-generated method stub

	}

	/* (non-Javadoc)
	 * @see javax.servlet.ServletContextListener#contextInitialized(javax.servlet.ServletContextEvent)
	 */
	public void contextInitialized(ServletContextEvent event) {
		// TODO Auto-generated method stub
        String logbackConfigLocation = event.getServletContext().getInitParameter(CONFIG_LOCATION);  
        String fn = event.getServletContext().getRealPath(logbackConfigLocation);  
        try {  
            LoggerContext loggerContext = (LoggerContext)LoggerFactory.getILoggerFactory();  
            loggerContext.reset();  
            JoranConfigurator joranConfigurator = new JoranConfigurator();  
            joranConfigurator.setContext(loggerContext);  
            joranConfigurator.doConfigure(fn);  
            logger.debug("loaded slf4j configure file from {}", fn);  
        }  
        catch (JoranException e) {  
            logger.error("can loading slf4j configure file from " + fn, e);  
        }  

	}

}