本文为大家分享了servlet监听器的具体学习内容，供大家参考，具体内容如下
1.什么是servlet监听器？
servlet监听器也叫web监听器。是servlet中一种特殊类。能够帮助开发者监听web应用中的特定事件。比如ServletContext，ServletSession，ServletRequest的创建和销毁，变量的创建和销毁等。
2 监听器常用的用途
通常使用Web监听器做以下的内容：
统计在线人数，利用HttpSessionLisener
加载初始化信息：利用ServletContextListener
统计网站访问量
实现访问监控
3.监听器的分类
根据servlet对象可以将监听器划分为三种：ServletContext，ServletSession,ServletRequest。
4监听器的应用
4.1 ServletContex :对应监控application内置对象的创建和销毁。
当web容器开启时，执行contextInitialized方法；当容器关闭或重启时，执行contextDestroyed方法。
实现方式：直接实现ServletContextListener接口
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package com.learn;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.io.*;
/**
* Created by Administrator on 2017/09/23.
*/
public class MyServletContextListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("Webapp initital.......");
ServletContext servletContext = sce.getServletContext();
InputStreamReader inputStreamReader = new InputStreamReader(servletContext.getResourceAsStream("/count/count.txt"));
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
try {
int icount = Integer.parseInt(bufferedReader.readLine());
icount++;
servletContext.setAttribute("count",icount);
System.out.println("Webapp initital success");
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("webApp destroyed ........");
ServletContext servletContext = sce.getServletContext();
Integer count = (Integer) servletContext.getAttribute("count");
if(count != null){
count ++;
String filePath = servletContext.getRealPath("/count");
filePath = filePath+"/count.txt";
try {
PrintWriter printWriter = new PrintWriter(filePath);
printWriter.write(count);
printWriter.close();
System.out.println("webApp desdroyed success ");
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
}
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4.2HttpSession监控：对应监控session内置对象的创建和销毁。
当打开一个新的页面时，开启一个session会话，执行sessionCreated方法；当页面关闭session过期时，或者容器关闭销毁时，执行sessionDestroyed方法。
实现方式：直接实现HttpSessionListener接口：
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package com.learn;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/**
* Created by Administrator on 2017/09/23.
*/
public class MySessionListener implements HttpSessionListener{
@Override
public void sessionCreated(HttpSessionEvent se) {
HttpSession session = se.getSession();
System.out.println("新建session，sessionId："+session.getId());
}
@Override
public void sessionDestroyed(HttpSessionEvent se) {
HttpSession session = se.getSession();
System.out.println("销毁session，sessionId："+session.getId());
}
}
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4.3ServletRequest监控：对应监控request内置对象的创建和销毁。
当访问某个页面时，出发一个request请求，执行requestInitialized方法；当页面关闭时，执行requestDestroyed方法。
实现方式，直接实现ServletRequestListener接口：
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package com.learn;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
/**
* Created by Administrator on 2017/09/23.
*/
public class MyRequestListener implements ServletRequestListener {
@Override
public void requestDestroyed(ServletRequestEvent sre) {
HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
Long date = System.currentTimeMillis()-(Long) (request.getAttribute("dateCreated"));
System.out.println("消耗时间："+date);
}
@Override
public void requestInitialized(ServletRequestEvent sre) {
HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
String uri = request.getRequestURI();
uri = request.getQueryString() == null ? uri : (uri + "?" + request.getQueryString());
request.setAttribute("dateCreated", System.currentTimeMillis());
System.out.println("IP:"+request.getRemoteAddr()+"URI:"+uri);
}
}
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5监听器web.xml的配置
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<listener>
<listener-class>com.learn.MyServletContextListener</listener-class>
</listener>
<listener>
<listener-class>com.learn.MySessionListener</listener-class>
</listener>
<listener>
<listener-class>com.learn.MyRequestListener</listener-class>
</listener>
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以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://www.cnblogs.com/wwyx-xi/p/7582515.html