JAVAEE listener总结

感觉比较简单，就不多说了，写一个案例就明白了。

用于显示当前在线的人的名字：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
  </head>
  
  <body>
     <form action="loginServlet" method="post">
          用户名： <input type="text" name="username"/><br/>
          <input type="submit" value="登录"><br/>
     </form>
  </body>
</html>

package com.huxin.listener;

import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class OnlineListener implements ServletContextListener,HttpSessionListener,HttpSessionAttributeListener{
    private ServletContext application = null;
	public void contextDestroyed(ServletContextEvent arg0) {}
	
	//初始化上下文时调用此方法
	public void contextInitialized(ServletContextEvent arg0) {
		System.out.println("load的时候调用此方法");
		//初始化application
		this.application = arg0.getServletContext();
		this.application.setAttribute("online", new ArrayList<String>());
		
	}
	
	//当session中的属性发生改变的时候调用此方法
	public void attributeAdded(HttpSessionBindingEvent arg0) {
		System.out.println("属性发生了改变，所以调用了方法");
		List<String> online = (List<String>)this.application.getAttribute("online");
		if("username".equals(arg0.getName())){
			online.add((String) arg0.getValue());
		}
		this.application.setAttribute("online", online);
	}
	
	public void attributeRemoved(HttpSessionBindingEvent arg0) {}
	public void attributeReplaced(HttpSessionBindingEvent arg0) {}
	public void sessionCreated(HttpSessionEvent arg0) {}
	
	//session被销毁的时候调用此方法
	public void sessionDestroyed(HttpSessionEvent arg0) {
		//销毁的时候调用此方法
System.out.println("销毁的时候调用此方法");
		List<String> online = (List<String>)this.application.getAttribute("online");
		String username = (String)arg0.getSession().getAttribute("username");
		online.remove(username);
		this.application.setAttribute("online", online);
	}
}

package com.huxin.web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
        request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		
		String username = request.getParameter("username");
System.out.println(username);

        if(username!=null&&!"".equals(username)){
        	request.getSession().setAttribute("username", username);
        }
        List<String> online = (List<String>)this.getServletContext().getAttribute("online");
        
		PrintWriter out = response.getWriter();
		out.println("当前的用户是："+ username+"<br/>");
		out.println("<hr>");
		out.println("<h3>当前的在线列表为</h3>");
		int size = online== null?0:online.size();
		for(int i = 0;i<size;i++){
			out.println(i+1+"." + online.get(i)+"<br/>");
		}
		out.println("<hr/><a href=\""+ response.encodeRedirectURL("logoutServlet")+"\">注销</a>");
		out.flush();
		out.close();
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
       this.doGet(request, response);
	}
}

package com.huxin.web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LogoutServlet extends HttpServlet {
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		
		this.doPost(req, resp);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
//		request.getSession().invalidate();
	    List<String> online = (List<String>)this.getServletContext().getAttribute("online");
	    
		PrintWriter out = response.getWriter();
		out.println((String)request.getSession().getAttribute("username"));
		out.println("<h3>当前的在线列表为</h3>");
		int size = online== null?0:online.size();
		for(int i = 0;i<size;i++){
			out.println(i+1+"." + online.get(i)+"<br/>");
		}
	}
}

web.xml中配置listener

  <listener>
     <listener-class>com.huxin.listener.OnlineListener</listener-class>
  </listener>

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